Filed Pursuant to Rule 424(b)(5)
Registration No. 333-222076

The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities and are not being used to solicit an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

Subject to Completion

Preliminary prospectus supplement dated December 13, 2018

PROSPECTUS SUPPLEMENT

(To prospectus dated December 15, 2017)

$326,000,000

Alliant Energy Corporation

Common Stock

The forward counterparties referred to below are offering $326,000,000 of shares of our common stock in this offering. We expect to enter into separate forward sale agreements with each of Goldman Sachs & Co. LLC and Bank of America N.A. or their respective affiliates, whom we refer to as the forward counterparties, in respect of $326,000,000 of shares of our common stock. In connection with the forward sale agreements between us and the forward counterparties, the forward counterparties or their respective affiliates are, at our request, borrowing from third parties and selling to the underwriters an aggregate of $326,000,000 of shares of our common stock that will be delivered in this offering. If in its good faith and commercially reasonable judgment, a forward counterparty is unable to borrow and deliver for sale on the anticipated closing date the number of shares of our common stock underlying the applicable forward sale agreement, or such forward counterparty would be unable to borrow, at a stock loan rate not greater than a specified rate, and deliver for sale on the anticipated closing date such number of shares of our common stock, or if certain other conditions to such forward counterparty’s obligations have not been satisfied, then we will issue and sell directly to the underwriters a number of shares of our common stock equal to the number of shares that such forward counterparty does not borrow and deliver.

We will not initially receive any proceeds from the sale of $326,000,000 of shares of our common stock sold by the forward counterparties to the underwriters, except in certain circumstances described in this prospectus supplement, including the last sentence of the previous paragraph. We expect to settle the forward sale agreements and receive proceeds, subject to certain adjustments, from the sale of those shares of common stock assuming one or more future physical settlements of the forward sale agreements no later than approximately 12 months after the date of this prospectus supplement. Although we expect to settle the forward sale agreements entirely by the full physical delivery of shares of our common stock in exchange for cash proceeds, we may elect cash settlement or net share settlement for all or a portion of our obligations under the forward sale agreements. If we elect to cash settle or net share settle the forward sale agreements, we may not receive any proceeds from the issuance of shares, and we will instead receive or pay cash (in the case of cash settlement) or receive or deliver shares of our common stock (in the case of net share settlement). See “Underwriting (Conflicts of Interest)” for a description of the forward sale agreements.

Our common stock is listed on the New York Stock Exchange, or the NYSE, under the symbol “LNT.” The last reported sale price of our common stock on the NYSE on December 12, 2018 was $45.89 per share.

Investing in our common stock involves risk. See “Risk Factors” on page S-5 of this prospectus supplement, page 4 of the accompanying prospectus and in the documents incorporated by reference into this prospectus supplement and the accompanying prospectus for a discussion of certain risks that prospective investors should consider before investing in our common stock.

The underwriters may offer shares of our common stock from time to time for sale in one or more transactions on the NYSE, in the over-the-counter market, through negotiated transactions or otherwise at market prices prevailing at the time of sale, at prices related to prevailing market prices or at negotiated prices. See “Underwriting (Conflicts of Interest).”

We have granted the underwriters an option to purchase up to an additional $48,900,000 of shares of our common stock, exercisable within 30 days from the date of this prospectus supplement. If such option is exercised, we may, in our sole discretion, enter into additional forward sale agreements with each of the forward counterparties in respect of the number of shares of our common stock that are subject to the exercise of such option, and we currently anticipate that, if such option is exercised, we will do so. Unless the context requires otherwise, the term “forward sale agreement” as used in this prospectus supplement includes any additional forward sale agreement that we elect to enter into in connection with the exercise by the underwriters of their option to purchase additional shares. In the event that we enter into any additional forward sale agreement, if in its good faith and commercially reasonable judgment, a forward counterparty is unable to borrow and deliver for sale on the anticipated closing date for the exercise of such option the number of shares of our common stock underlying the applicable forward sale agreement, or such forward counterparty would be unable to borrow, at a stock loan rate not greater than a specified rate, and deliver for sale on the anticipated closing date such number of shares of our common stock, or if certain other conditions to such forward counterparty’s obligations have not been satisfied, then we will issue and sell directly to the underwriters a number of shares of our common stock equal to the number of shares that such forward counterparty does not borrow and deliver.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is accurate or complete. Any representation to the contrary is a criminal offense.

The underwriters expect to deliver the shares on or about December     , 2018.

The date of this prospectus supplement is December     , 2018.

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

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ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering of common stock. The second part, the accompanying prospectus, gives more general information, some of which may not apply to this offering. You should read the entire prospectus supplement, as well as the accompanying prospectus and the documents incorporated by reference that are described under “Where You Can Find More Information” in this prospectus supplement. In the event that the description of the offering varies between this prospectus supplement and the accompanying prospectus, you should rely on the information contained in this prospectus supplement. Generally, when we refer to the “prospectus,” we are referring to this prospectus supplement and the accompanying prospectus combined.

Any statement made in this prospectus or in a document incorporated or deemed to be incorporated by reference into this prospectus will be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus or any subsequently filed document that is also incorporated by reference into this prospectus modifies or supersedes that statement. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

You should rely only on the information contained or incorporated by reference in this prospectus or any “free writing prospectus” we may authorize to be delivered to you. “Incorporated by reference” means that we can disclose important information to you by referring you to another document filed separately with the Securities and Exchange Commission, or the SEC. We have not authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not making an offer to sell nor soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus and the documents incorporated by reference is accurate only as of the respective dates of those documents in which the information is contained. Our business, financial condition, results of operations and prospects may have changed since any such date.

Unless we otherwise indicate or unless the context requires otherwise, all references in this prospectus supplement to “Alliant Energy,” “we,” “our,” “us” or similar references mean Alliant Energy Corporation.

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FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the information incorporated by reference herein or therein contain forward-looking statements intended to qualify for the safe harbor from liability established by the Private Securities Litigation Reform Act of 1995. All statements, other than statements of historical fact, included in this prospectus supplement or the accompanying prospectus or incorporated by reference herein or therein, including statements regarding anticipated financial performance, business strategy and management’s plans and objectives for future operations, are forward-looking statements. These forward-looking statements can be identified as such because the statements include words such as “may,” “believe,” “expect,” “anticipate,” “plan,” “project,” “will,” “projections,” “estimate,” or other words of similar import. These forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from those expressed in, or implied by, such statements. Readers are cautioned not to place undue reliance on these forward-looking statements. All forward-looking statements included in this prospectus supplement, the accompanying prospectus or in a document incorporated by reference herein or therein speak only as of the date of this prospectus supplement, the accompanying prospectus or the document incorporated by reference, as the case may be. Additional information concerning factors that could cause actual results to differ materially from those in the forward-looking statements is contained under “Risk Factors” on page S-5 of this prospectus supplement, page 4 of the accompanying prospectus and other documents that we file from time to time with the SEC that are incorporated by reference into this prospectus supplement and the accompanying prospectus, including, but not limited to, the risk factor disclosure beginning on page 14 of our Annual Report on Form 10-K for the fiscal year ended December 31, 2017. Some, but not all, of the risks and uncertainties that could materially affect actual results include:

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We assume no obligation, and disclaim any duty, to update or revise publicly any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

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RISK FACTORS

Investing in our common stock involves risk. You should carefully consider the following risk factors together with all the other information contained in this prospectus supplement or incorporated by reference in this prospectus. You should also consider the risks and uncertainties discussed under the caption “Risk Factors” included in our Annual Report on Form 10-K for the year ended December 31, 2017, which is incorporated by reference in this prospectus supplement, and which may be amended, supplemented or superseded from time to time by other reports we file with the SEC in the future.

Settlement provisions contained in the forward sale agreements could result in substantial dilution to our earnings per share and return on equity or result in substantial cash payment obligations.

Each forward counterparty will have the right to accelerate the applicable forward sale agreement (with respect to a transaction under that particular forward sale agreement that the relevant forward counterparty determines is affected by such event) and require us to physically settle or, if we so elect and the forward counterparty permits our election, cash settle or net share settle on a date specified by the relevant forward counterparty if:

A forward counterparty’s decision to exercise its right to accelerate the settlement of a particular forward sale agreement will be made irrespective of our need for capital. In such cases, we could be required to issue and deliver shares of common stock under the physical settlement provisions of that particular forward sale agreement or, if we so elect and the forward counterparty permits our election, net share settlement provisions of that particular forward sale agreement irrespective of our capital needs, which would result in dilution to our earnings per share and return on equity.

We expect that settlement of the forward sale agreements will occur no later than December 31, 2019. However, any forward sale agreement may be settled earlier in whole or in part at our option. We expect that

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each forward sale agreement will be physically settled by delivery of shares of our common stock, unless we elect to cash settle or net share settle a particular forward sale agreement. Upon physical settlement or, if we so elect, net share settlement of a particular forward sale agreement, delivery of shares of our common stock in connection with such physical settlement or (to the extent we are obligated to deliver shares of our common stock) net share settlement will result in dilution to our earnings per share and return on equity. If we elect cash settlement or net share settlement with respect to all or a portion of the shares of common stock underlying a particular forward sale agreement, we expect that the relevant forward counterparty (or an affiliate thereof) will purchase a number of shares of common stock necessary to satisfy its or its affiliate’s obligation to return the shares of common stock borrowed from third parties in connection with sales of shares of our common stock related to that forward sale agreement. In addition, the purchase of shares of our common stock in connection with the relevant forward counterparty or its affiliate unwinding its hedge positions could cause the price of our common stock to increase over such time (or prevent a decrease over such time), thereby increasing the amount of cash we would owe to the relevant forward counterparty (or decreasing the amount of cash that the relevant forward counterparty would owe us) upon a cash settlement of the relevant forward sale agreement or increasing the number of shares of common stock we would deliver to the relevant forward counterparty (or decreasing the number of shares of common stock that the relevant forward counterparty would deliver to us) upon net share settlement of the relevant forward sale agreement.

The forward sale price that we expect to receive upon physical settlement of a particular forward sale agreement will be subject to increase or decrease based on the federal funds rate less a spread, and subject to price adjustment and other provisions of the forward sale agreements, including a decrease based on amounts related to expected dividends on our common stock on each of certain dates specified in the forward sale agreements and if the cost to the forward counterparty of borrowing a number of shares of our common stock underlying the forward sale agreement exceeds a specified amount. If the federal funds rate is less than the spread on any day, the interest factor will result in a daily reduction of the applicable forward sale price. If the market value of our common stock during the relevant valuation period under the particular forward sale agreement is above the applicable forward sale price, in the case of cash settlement, we would pay the relevant forward counterparty under that particular forward sale agreement an amount in cash equal to the difference or, in the case of net share settlement, we would deliver to the relevant forward counterparty a number of shares of common stock having a value equal to the difference. Thus, we could be responsible for a potentially substantial cash payment in the case of cash settlement of a particular forward sale agreement. See “Underwriting (Conflicts of Interest)” for a description of the forward sale agreements.

In case of our bankruptcy or insolvency, any forward sale agreements will automatically terminate, and we would not receive the expected proceeds from any forward sales of our common stock.

If we file for or consent to a proceeding seeking a judgment in bankruptcy or insolvency or any other relief under any bankruptcy or insolvency law or other similar law affecting creditors’ rights, or we or a regulatory authority with jurisdiction over us presents a petition for our winding-up or liquidation, and we consent to such a petition, any forward sale agreements that are then in effect will automatically terminate. If any such forward sale agreement so terminates under these circumstances, we would not be obligated to deliver to the relevant forward counterparty any of our common stock not previously delivered, and the relevant forward counterparty would be discharged from its obligation to pay the applicable forward sale price per share in respect of any of our common stock not previously settled under the applicable forward sale agreement. Therefore, to the extent that there are any shares of our common stock with respect to which any forward sale agreement has not been settled at the time of the commencement of any such bankruptcy or insolvency proceedings, we would not receive the relevant forward sale price per share in respect of those shares of our common stock.

Sales of a substantial number of shares of our common stock, or the perception that such sales might occur, could adversely affect the trading price of our common stock.

As of December 11, 2018, we had 236,057,526 shares of our common stock outstanding. Also, we had, as of December 11, 2018, approximately 11.2 million shares of common stock in the aggregate reserved for issuance pursuant to our Amended and Restated 2010 Omnibus Incentive Plan, Shareowner Direct Plan and 401(k)

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Savings Plan. The issuance of any common stock by us pursuant to a forward sale agreement upon physical settlement or net share settlement thereof, or in lieu of the forward counterparties selling our common stock to the underwriters as further described elsewhere in this prospectus supplement, will increase the number of shares of common stock that we have outstanding. Sales of a substantial number of shares of our common stock, or the perception that such sales might occur, could adversely affect the trading price of our common stock. Further, issuance of shares pursuant to our Amended and Restated 2010 Omnibus Incentive Plan, our Shareowner Direct Plan or our 401(k) Savings Plan, or the perception in the market that the holders of a large number of shares intend to sell shares, could reduce the market price of our common stock.

You may experience dilution.

The issuance of any common stock by us pursuant to a forward sale agreement upon physical settlement or net share settlement thereof, or in lieu of the forward counterparties selling our common stock to the underwriters as further described elsewhere in this prospectus supplement, may have a dilutive effect on our expected earnings per weighted average share. The actual amount of dilution cannot be determined at this time and will be based on a number of factors. Also, except for the lock-up restrictions we have agreed to in connection with this offering, we are not restricted from issuing additional securities in the future, including shares of common stock, securities that are convertible into or exchangeable for, or that represent the right to receive, common stock or substantially similar securities. See “Underwriting (Conflicts of Interest)—Lock-Ups.” The price per share at which we sell additional shares of our common stock, or securities convertible or exchangeable into common stock, in future transactions may be higher or lower than the price per share paid by investors in this offering and investors purchasing shares or other securities in the future could have rights superior to existing shareowners. The issuance of these securities may cause further dilution to our shareowners.

The market price of our common stock may fluctuate significantly.

The market price of our common stock could be subject to significant fluctuations in response to factors such as the following, some of which are beyond our control:

In addition, the stock markets in general, including the NYSE, are subject to significant price and trading fluctuations. These fluctuations have resulted in volatility in the market prices of securities that often has been unrelated or disproportionate to changes in operating performance and may affect adversely the market price of our common stock.

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USE OF PROCEEDS

We will not initially receive any proceeds from the sale of shares of our common stock by the forward counterparties or their affiliates, unless an event occurs that requires us to sell our common stock to the underwriters in lieu of a forward counterparty borrowing and delivering shares of our common stock to the underwriters, in which case we intend to use all net proceeds we receive from such sale for the same purposes described below. We currently anticipate that if the underwriters exercise their option to purchase additional shares, we will request that the forward counterparties borrow such additional shares from third parties and sell such shares to the underwriters, and that we will enter into additional forward sale agreements with the forward counterparties in connection therewith.

At an initial forward sale price of $         per share (which is the price at which the underwriters have agreed to buy the shares of common stock offered hereby), we expect to receive net proceeds, before expenses, of approximately $         million (or approximately $         million if the underwriters’ option to purchase additional shares of our common stock is exercised in full), subject to the price adjustment and other provisions of the forward sale agreements, in the event of full physical settlement of the forward sale agreements, which settlement must occur within approximately 12 months of the date of this prospectus supplement. For purposes of calculating the proceeds to us upon settlement of the forward sale agreements, we have assumed that each forward sale agreement is physically settled based upon the initial forward sale price of $         (which is the price at which the underwriters have agreed to buy the shares of common stock offered hereby) on the effective date of the forward sale agreements, which will be December     , 2018. The actual proceeds from the forward sales are subject to the final settlement of the forward sale agreements. The forward sale price that we expect to receive upon physical settlement of the forward sale agreements will be subject to adjustment on a daily basis based on a floating interest rate factor equal to the federal funds rate less a spread and will be decreased on each of certain dates specified in each forward sale agreement during the term of such forward sale agreement. The forward sale price will also be subject to decrease if the cost to the forward counterparty of borrowing a number of shares of our common stock underlying the forward sale agreement exceeds a specified amount. If the federal funds rate is less than the spread on any day, the interest factor will result in a daily reduction of the forward sale price. See “Underwriting (Conflicts of Interest)—Forward Sale Agreements” for a description of the forward sale agreements.

We intend to use the net proceeds we receive upon the issuance and sale of shares of our common stock for general corporate purposes, which may include repayment or refinancing of debt, working capital, construction and acquisition expenditures, investments and repurchases and redemptions of securities.

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UNDERWRITING (CONFLICTS OF INTEREST)

In this offering, subject to the terms and conditions of the underwriting agreement, the forward counterparties have agreed, at our request, to borrow from third parties and sell to the underwriters $326,000,000 of shares of our common stock in connection with the execution of forward sale agreements between us and each of Goldman Sachs & Co. LLC and Bank of America, N.A., whom we refer to in such capacity as the forward counterparties. Subject to the terms and conditions of the underwriting agreement among us, the forward counterparties and the underwriters, the forward counterparties have agreed to sell to the underwriters named below, and the underwriters named below have severally agreed to purchase from the forward counterparties, the number of shares of our common stock listed opposite their names below:

The underwriters have agreed to purchase all of the shares of common stock sold under the underwriting agreement if they purchase any shares. The underwriting agreement provides that the obligations of the underwriters to purchase the shares included in this offering are subject to approval of legal matters by counsel and to other conditions contained in the underwriting agreement.

The following table shows the per share and total underwriting discounts and commissions to be paid to the underwriters assuming both no exercise and full exercise of the underwriters’ option to purchase additional shares.

We estimate that the total expenses of this offering payable by us, excluding underwriting discounts and commissions, will be approximately $         million.

The underwriters propose to initially offer the shares of common stock directly to the public at the public offering price set forth on the cover page of this prospectus supplement and to certain dealers at that price less a concession not in excess of $         per share. After the offering of the shares to the public, the offering price and other selling terms may be changed by the underwriters. Sales of the shares made outside the United States may be made by affiliates of the underwriters.

We have agreed to indemnify the several underwriters against, or contribute to payments that the underwriters may be required to make in respect of, certain liabilities, including liabilities under the Securities Act of 1933, as amended, or the Securities Act.

The underwriters propose to offer the shares of common stock offered hereby from time to time for sale in one or more transactions on the NYSE, in the over-the-counter market, through negotiated transactions or otherwise at market prices prevailing at the time of sale, at prices related to prevailing market prices or at negotiated prices, subject to receipt and acceptance by them and subject to their right to reject any order in whole

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or in part. The underwriters may effect such transactions by selling the shares of common stock to or through dealers and such dealers may receive compensation in the form of discounts, concessions or commissions from the underwriters and/or purchasers of shares of common stock for whom they may act as agents or to whom they may sell as principal. The difference between the price at which the underwriters purchase shares and the price at which the underwriters resell such shares may be deemed underwriting compensation.

Forward Sale Agreements

We expect to enter into forward sale agreements on the date of this prospectus supplement with the forward counterparties relating to an aggregate of $326,000,000 of shares of our common stock. In connection with the execution of the forward sale agreements, and at our request, the forward counterparties are borrowing from third parties and selling in this offering an aggregate of $326,000,000 of shares of our common stock.

If in the good faith and commercially reasonable judgment of a forward counterparty, (i) it or its affiliate is unable to borrow and deliver for sale on the anticipated closing date of the offering the full number of shares of our common stock underlying the applicable forward sale agreement, or (ii) it or its affiliate is unable to borrow, at a stock loan rate not greater than a specified rate, and deliver for sale on the anticipated closing date of the offering the full number of shares of our common stock underlying the applicable forward sale agreement, then the number of shares of our common stock to which such forward sale agreement relates will be reduced to the number that such forward counterparty can so borrow and deliver, which may be zero. In the event that the number of shares of our common stock to which one or more of the forward sale agreements relate is so reduced, the commitments of the several underwriters to purchase shares of our common stock from the forward counterparties and the forward counterparties’ obligation to borrow such shares for delivery and sale to the several underwriters, as described above, will be replaced with the commitments to purchase from us and our corresponding obligation to issue directly to the underwriters, severally in proportion to their respective underwriting obligations reflected in the table above, all or such portion of the number of shares of our common stock not borrowed and delivered by the forward counterparties. In such event, we or the representatives of the underwriters will have the right to postpone the closing date for up to two business days to effect any necessary changes to the documents or arrangements in connection with such closing.

We will receive an amount equal to the net proceeds from the sale of the borrowed shares of our common stock sold in this offering, subject to certain adjustments pursuant to the forward sale agreements, from the forward counterparties upon physical settlement of the forward sale agreements. We will only receive such proceeds if we elect to physically settle the forward sale agreements.

The forward sale agreements provide for settlement on a settlement date or dates to be specified at our discretion, but which we expect to occur on or prior to December 31, 2019. On a settlement date or dates, if we decide to physically settle one or more forward sale agreements, we will issue shares of our common stock to the relevant forward counterparty at the then-applicable forward sale price. The forward sale price will initially be $         per share, which is the price at which the underwriters have agreed to buy the shares of common stock offered hereby. The forward sale agreements provide that the initial forward sale price will be subject to adjustment based on a floating interest rate factor equal to the federal funds rate less a spread, and will be subject to decrease on each of certain dates specified in the forward sale agreements by amounts related to expected dividends on shares of our common stock during the term of the forward sale agreements. The forward sale price will also be subject to decrease if the cost to the forward counterparty of borrowing a number of shares of our common stock underlying the forward sale agreement exceeds a specified amount. If the federal funds rate is less than the spread on any day, the interest rate factor will result in a daily reduction of the forward sale price.

Before any issuance of shares of our common stock upon physical or net share settlement of the forward sale agreements, we expect that the shares issuable upon settlement of the forward sale agreements will be reflected in our diluted earnings per share calculation using the treasury stock method. Under this method, the number of shares of our common stock used in calculating diluted earnings per share is deemed to be increased by the excess, if any, of the number of shares of common stock that would be issued upon full physical settlement of the forward sale

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agreements over the number of shares of common stock that could be purchased by us in the market (based on the average market price of our common stock during the applicable reporting period) using the proceeds receivable upon full physical settlement (based on the adjusted forward sale price at the end of the reporting period). Consequently, prior to physical or net share settlement of the forward sale agreements and subject to the occurrence of certain events, we anticipate there will be no dilutive effect on our earnings per share except during periods when the average market price of shares of our common stock is above the applicable adjusted forward sale price, which is initially $             (which is the price at which the underwriters agree to buy the shares of our common stock offered hereby), subject to increase or decrease based on the federal funds rate less a spread, and subject to price adjustment and other provisions of the forward sale agreements, including a decrease based on amounts related to expected dividends on our common stock on each of certain dates specified in the forward sale agreements and if the cost to the forward counterparty of borrowing a number of shares of our common stock underlying the forward sale agreement exceeds a specified amount. However, if we decide to physically settle or net share settle the forward sale agreements, delivery of shares of our common stock to the forward counterparties on any such physical or net share settlement of the forward sale agreements would result in dilution to our earnings per share.

Each forward counterparty will have the right to accelerate that particular forward sale agreement (with respect to a transaction under that particular forward sale agreement that the relevant forward counterparty determines is affected by such event) and require us to physically settle or, if we so elect and the forward counterparty permits our election, cash settle or net share settle on a date specified by the relevant forward counterparty if:

A forward counterparty’s decision to exercise its right to accelerate the settlement of a particular forward sale agreement will be made irrespective of our need for capital. In such cases, we could be required to issue and deliver shares of common stock under the physical settlement provisions of that particular forward sale agreement or, if we so elect and the forward counterparty permits our election, net share settlement provisions of that particular forward sale agreement irrespective of our capital needs, which would result in dilution to our earnings per share and return on equity. In addition, upon certain events of bankruptcy or insolvency related to us, each forward sale agreement will automatically terminate without further liability of either party. Following any such termination, we would not issue any shares of common stock or receive any proceeds pursuant to the forward sale agreements.

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Each forward sale agreement will be physically settled, unless we elect to settle such forward sale agreement in cash or to net share settle such forward sale agreement (which we have the right to do, subject to certain conditions, other than in the limited circumstances described above). If we decide to physically settle or net share settle a forward sale agreement, delivery of shares of our common stock upon any physical settlement or net share settlement of the forward sale agreement will result in dilution to our earnings per share. If we elect cash or net share settlement for all or a portion of the shares of our common stock underlying a forward sale agreement, we would expect the relevant forward counterparty or one of its affiliates to repurchase a number of shares of our common stock equal to the portion for which we elect cash or net share settlement in order to satisfy its obligation to return the shares of our common stock such forward counterparty had borrowed in connection with sales of our common stock under this prospectus supplement and, if applicable in connection with net share settlement, to deliver shares of our common stock to us. If the market value of our common stock at the time of such purchase is above the forward sale price at that time, we will pay or deliver, as the case may be, to the relevant forward counterparty under its forward sale agreement, an amount in cash, or a number of shares of our common stock with a market value, equal to such difference. Any such difference could be significant. Conversely, if the market value of our common stock at the time of such purchase is below the forward sale price at that time, such forward counterparty will pay or deliver, as the case may be, to us under its forward sale agreement, an amount in cash, or a number of shares of our common stock with a market value, equal to such difference.

In addition, the purchase of shares of our common stock by a forward counterparty or its affiliate to unwind such forward counterparty’s hedge position could cause the market price of our common stock to increase over time, thereby increasing the amount of cash we would owe to a forward counterparty upon a cash settlement or increasing the number of shares of our common stock we would owe to a forward counterparty upon a net share settlement, as the case may be, of its forward sale agreement, or decreasing the amount of cash that a forward counterparty would owe us upon a cash settlement or decreasing the number of shares of our common stock that a forward counterparty would owe us upon a net share settlement, as the case may be, of its forward sale agreement. We will not be able to control the manner in which the forward counterparties unwind their hedge positions.

The foregoing is a description of certain provisions of the forward sale agreements we expect to enter into in connection with this offering, copies of which are available upon request from us at the address set forth in the section of the accompanying prospectus entitled “Where You Can Find More Information.” This description of certain terms of the forward sale agreements is not complete and is subject to, and qualified in its entirety by reference to, the provisions of those agreements.

Option to Purchase Additional Shares

We have granted the underwriters an option for a period of 30 days from the date of this prospectus supplement to purchase up to an additional $48,900,000 of shares of our common stock at a price of $         per share. If such option is exercised, we may, in our sole discretion, enter into additional forward sale agreements with each of the forward counterparties in respect of the number of shares of our common stock that are subject to the exercise of such option, and we currently anticipate that, if such option is exercised, we will do so. If such option is exercised and we elect not to enter into additional forward sale agreements, we have agreed to issue and sell directly to the underwriters the number of shares of our common stock that are subject to the exercise of such option. In the event that we enter into any additional forward sale agreement, if in its good faith and commercially reasonable judgment, a forward counterparty or its affiliate is unable to borrow and deliver for sale on the anticipated closing date for the exercise of such option the number of shares of our common stock underlying the applicable forward sale agreement, or such forward counterparty would be unable to borrow, at a stock loan rate not greater than a specified rate, and deliver for sale on the anticipated closing date such number of shares of our common stock, or if certain other conditions to such forward counterparty’s obligations have not been satisfied, then we will issue and sell directly to the underwriters a number of shares of our common stock equal to the number of shares that such forward counterparty does not borrow and deliver.

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Lock-Ups

We and all of our directors and executive officers have agreed, subject to certain exceptions, for a period of 60 days after the date of this prospectus supplement, to not, without the prior written consent of the underwriters, (1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, or cause to be filed with the SEC a registration statement under the Securities Act relating to, any shares of common stock or any securities convertible into or exercisable or exchangeable for common stock, or publicly disclose the intention to make any offer, sale, pledge or disposition, (2) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the common stock or such other securities, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of common stock or such other securities, in cash or otherwise. The foregoing restrictions do not apply, in our case, to the issuance of any common stock by us pursuant to a forward sale agreement upon physical settlement or net share settlement thereof, or in lieu of the forward counterparties selling our common stock to the underwriters as further described elsewhere in this prospectus supplement; any common stock issuable upon the exercise of options, or upon the vesting of restricted stock units or performance restricted stock units, granted under our equity incentive plans (as existing on the date hereof); the grant of restricted stock units or performance restricted stock unit awards under our equity incentive plans; and common stock issued pursuant to our Amended and Restated 2010 Omnibus Incentive Plan, our Shareowner Direct Plan or our 401(k) Savings Plan. The foregoing restrictions also do not apply, with respect to our directors and executive officers, to withholding of shares by us for the purpose of covering tax liabilities related to vesting of restricted stock unit awards during the 60-day period and to transfers of shares as gifts, by will or the laws of intestacy, or pursuant to domestic relations or court orders.

Price Stabilization and Short Positions

In connection with this offering, the underwriters may engage in stabilizing transactions, which involves making bids for, purchasing and selling shares of common stock in the open market for the purpose of preventing or retarding a decline in the market price of the common stock while this offering is in progress. These stabilizing transactions may include making short sales of the common stock, which involves the sale by the underwriters of a greater number of shares of common stock than they are required to purchase in this offering, and purchasing shares of common stock on the open market to cover positions created by short sales. The underwriters may close out any short position by purchasing shares in the open market. A short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of the common stock in the open market that could adversely affect investors who purchase in this offering. To the extent that the underwriters create a short position, they will purchase shares in the open market to cover the position.

The underwriters have advised us that, pursuant to Regulation M of the Securities Act, they may also engage in other activities that stabilize, maintain or otherwise affect the price of the common stock, including the imposition of penalty bids. This means that if the underwriters purchase common stock in the open market in stabilizing transactions or to cover short sales the underwriters that sold those shares as part of this offering may be required to repay the underwriting discount received by them.

These activities may have the effect of raising or maintaining the market price of the common stock or preventing or retarding a decline in the market price of the common stock, and, as a result, the price of the common stock may be higher than the price that otherwise might exist in the open market. If the underwriters commence these activities, they may discontinue them at any time. The underwriters may carry out these transactions on the NYSE, in the over the counter market or otherwise.

Certain Relationships

The underwriters and their respective affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory

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investment management, investment research, principal investment, hedging, financing and brokerage activities. In the ordinary course of business, certain of the underwriters or their respective affiliates have provided and may in the future provide commercial, financial advisory or investment banking services for us and our subsidiaries for which they have received or will receive customary compensation. In particular, among other relationships, affiliates of the underwriters are lenders under our credit facility.

In the ordinary course of their various business activities, the underwriters and their respective affiliates have made or held, and may in the future make or hold, a broad array of investments including serving as counterparties to certain derivative and hedging arrangements, and may have actively traded, and, in the future may actively trade, debt and equity securities (or related derivative securities), and financial instruments (including bank loans) for their own account and for the accounts of their customers and may have in the past and at any time in the future hold long and short positions in such securities and instruments. Such investment and securities activities may have involved, and in the future may involve, securities and instruments of us or our subsidiaries. The underwriters and their respective affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Conflicts of Interest

All of the proceeds from the sale of shares of our common stock offered by the forward counterparties in this offering (excluding proceeds, if any, paid to us with respect to any shares of common stock that we may sell to the underwriters in lieu of the forward counterparties selling such shares as further described elsewhere in this prospectus supplement) will be paid to the forward counterparties. Because Goldman Sachs & Co. LLC and Merrill Lynch, Pierce, Fenner & Smith Incorporated, or their affiliates, in their capacity as forward purchasers, will receive more than 5% of the net proceeds of this offering, Goldman Sachs & Co. LLC and Merrill Lynch, Pierce, Fenner & Smith Incorporated are deemed to have a conflict of interest within the meaning of FINRA Rule 5121. Accordingly, this offering will be conducted in compliance with the applicable provisions of FINRA Rule 5121. Pursuant to that rule, the appointment of a “qualified independent underwriter” is not required in connection with this offering, as the shares of common stock have a “bona fide public market” (as defined in FINRA Rule 5121).

Electronic Prospectus Delivery

A prospectus supplement and accompanying base prospectus in electronic format may be made available on the web sites maintained by one or more underwriters, or selling group members, if any, participating in the offering. The underwriters may agree to allocate a number of shares to underwriters and selling group members for sale to their online brokerage account holders. Internet distributions will be allocated by the underwriters and selling group members that may make Internet distributions on the same basis as other allocations.

Selling Restrictions

Other than in the United States, no action has been taken by us or the underwriters that would permit a public offering of the shares of common stock offered by this prospectus supplement in any jurisdiction where action for that purpose is required. The shares of common stock offered by this prospectus supplement may not be offered or sold, directly or indirectly, nor may this prospectus supplement or any other offering material or advertisements in connection with the offer and sale of any such of common stock be distributed or published in any jurisdiction, except under circumstances that will result in compliance with the applicable rules and regulations of that jurisdiction. Persons into whose possession this prospectus supplement comes are advised to inform themselves about and to observe any restrictions relating to the offering and the distribution of this prospectus supplement. This prospectus supplement does not constitute an offer to sell or a solicitation of an offer to buy any shares of common stock offered by this prospectus supplement in any jurisdiction in which such an offer or a solicitation is unlawful.

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European Economic Area

In relation to each member state of the European Economic Area (each, a “Member State”), no offer of shares of common stock that are the subject of the offering has been, or will be made to the public in that Member State, other than under the following exemptions under the Prospectus Directive:

provided that no such offer of shares of common stock referred to in (a) to (c) above shall result in a requirement for us or any underwriter to publish a prospectus pursuant to Article 3 of the Prospectus Directive, or supplement a prospectus pursuant to Article 16 of the Prospectus Directive.

Each person located in a Member State to whom any offer of shares of common stock is made or who receives any communication in respect of an offer of shares of common stock, or who initially acquires any shares of common stock will be deemed to have represented, warranted, acknowledged and agreed to and with each underwriter and us that (1) it is a “qualified investor” within the meaning of the law in that Member State implementing Article 2(1)(e) of the Prospectus Directive; and (2) in the case of any shares of common stock acquired by it as a financial intermediary as that term is used in Article 3(2) of the Prospectus Directive, the shares of common stock acquired by it in the offer have not been acquired on behalf of, nor have they been acquired with a view to their offer or resale to, persons in any Member State other than qualified investors, as that term is defined in the Prospectus Directive, or in circumstances in which the prior consent of the underwriters has been given to the offer or resale; or where shares of common stock have been acquired by it on behalf of persons in any Member State other than qualified investors, the offer of those shares of common stock to it is not treated under the Prospectus Directive as having been made to such persons.

We, the underwriters and their respective affiliates will rely upon the truth and accuracy of the foregoing representations, acknowledgments and agreements.

This prospectus supplement has been prepared on the basis that any offer of shares of common stock in any Member State will be made pursuant to an exemption under the Prospectus Directive from the requirement to publish a prospectus for offers of shares. Accordingly any person making or intending to make an offer in that Member State of shares of common stock that are the subject of the offering contemplated in this prospectus supplement may only do so in circumstances in which no obligation arises for us or any of the underwriters to publish a prospectus pursuant to Article 3 of the Prospectus Directive in relation to such offer. Neither we nor the underwriters have authorized, nor do they authorize, the making of any offer of shares of common stock in circumstances in which an obligation arises for us or the underwriters to publish a prospectus for such offer.

For the purposes of this provision, the expression an “offer of shares of common stock to the public” in relation to any shares of common stock in any Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the shares of common stock to be offered so as to enable an investor to decide to purchase or subscribe the shares of common stock, as the same may be varied in that Member State by any measure implementing the Prospectus Directive in that Member State, the expression “Prospectus Directive” means Directive 2003/71/EC (as amended) and includes any relevant implementing measure in each Member State.

The above selling restriction is in addition to any other selling restrictions set out below.

United Kingdom

In addition, in the United Kingdom, this document is being distributed only to, and is directed only at, and any offer subsequently made may only be directed at, persons who are “qualified investors” (as defined in the

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Prospectus Directive) (i) who have professional experience in matters relating to investments falling within Article 19 (5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended (the “Order”) and/or (ii) who are high net worth companies (or persons to whom it may otherwise be lawfully communicated) falling within Article 49(2)(a) to (d) of the Order (all such persons together being referred to as “relevant persons”). This document must not be acted on or relied on in the United Kingdom by persons who are not relevant persons. In the United Kingdom, any investment or investment activity to which this document relates is only available to, and will be engaged in with, relevant persons.

Australia

No placement document, prospectus, product disclosure statement or other disclosure document has been lodged with the Australian Securities and Investments Commission (“ASIC”), in relation to the offering. This prospectus supplement does not constitute a prospectus, product disclosure statement or other disclosure document under the Corporations Act 2001 (the “Corporations Act”), and does not purport to include the information required for a prospectus, product disclosure statement or other disclosure document under the Corporations Act.

Any offer in Australia of the shares of common stock may only be made to persons (the “Exempt Investors”) who are “sophisticated investors” (within the meaning of section 708(8) of the Corporations Act), “professional investors” (within the meaning of section 708(11) of the Corporations Act) or otherwise pursuant to one or more exemptions contained in section 708 of the Corporations Act so that it is lawful to offer the shares of common stock without disclosure to investors under Chapter 6D of the Corporations Act.

The shares of common stock applied for by Exempt Investors in Australia must not be offered for sale in Australia in the period of 12 months after the date of allotment under the offering, except in circumstances where disclosure to investors under Chapter 6D of the Corporations Act would not be required pursuant to an exemption under section 708 of the Corporations Act or otherwise or where the offer is pursuant to a disclosure document which complies with Chapter 6D of the Corporations Act. Any person acquiring shares of common stock must observe such Australian on-sale restrictions.

This prospectus supplement contains general information only and does not take account of the investment objectives, financial situation or particular needs of any particular person. It does not contain any securities recommendations or financial product advice. Before making an investment decision, investors need to consider whether the information in this prospectus supplement is appropriate to their needs, objectives and circumstances, and, if necessary, seek expert advice on those matters.

Bermuda

Shares of common stock may be offered or sold in Bermuda only in compliance with the provisions of the Investment Business Act of 2003 of Bermuda which regulates the sale of securities in Bermuda. Additionally, non-Bermudian persons (including companies) may not carry on or engage in any trade or business in Bermuda unless such persons are permitted to do so under applicable Bermuda legislation.

British Virgin Islands

The shares of common stock may be offered to persons located in the British Virgin Islands who are “qualified investors” for the purposes of the Securities and Investment Business Act, 2010 (“SIBA”). Qualified investors include (i) certain entities which are regulated by the Financial Services Commission in the British Virgin Islands, including banks, insurance companies, licensees under SIBA and public, professional and private mutual funds; (ii) a company, any securities of which are listed on a recognised exchange; and (iii) persons defined as “professional investors” under SIBA, which is any person (a) whose ordinary business involves, whether for that person’s own account or the account of others, the acquisition or disposal of property of the

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same kind as the property, or a substantial part of our property; or (b) who has signed a declaration that the person, whether individually or jointly with the person’s spouse, has net worth in excess of US$1,000,000 and that the person consents to being treated as a professional investor.

Canada

The shares of common stock may be sold only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the shares of common stock must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus supplement (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 (or, in the case of securities issued or guaranteed by the government of a non-Canadian jurisdiction, section 3A.4) of National Instrument 33-105 Underwriting Conflicts (NI 33-105), the underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

China

This prospectus supplement does not constitute a public offer of shares of common stock, whether by sale or subscription, in the People’s Republic of China (the “PRC”). The shares of common stock are not being offered or sold directly or indirectly in the PRC to or for the benefit of, legal or natural persons of the PRC.

Further, no legal or natural persons of the PRC may directly or indirectly purchase any of the shares of common stock or any beneficial interest therein without obtaining all prior PRC’s governmental approvals that are required, whether statutorily or otherwise. Persons who come into possession of this document are required by us and our representatives to observe these restrictions.

Dubai International Financial Centre

This prospectus supplement relates to an Exempt Offer in accordance with the Offered Securities Rules of the Dubai Financial Services Authority (“DFSA”). This prospectus supplement is intended for distribution only to persons of a type specified in the Offered Securities Rules of the DFSA. It must not be delivered to, or relied on by, any other person. The DFSA has no responsibility for reviewing or verifying any documents in connection with Exempt Offers. The DFSA has not approved this prospectus supplement nor taken steps to verify the information set forth herein and has no responsibility for the prospectus supplement. The shares of common stock to which this prospectus supplement relates may be illiquid and/or subject to restrictions on their resale. Prospective purchasers of the shares of common stock offered should conduct their own due diligence on the shares of common stock. If you do not understand the contents of this prospectus supplement you should consult an authorized financial advisor.

Hong Kong

The shares of common stock have not been offered or sold and will not be offered or sold in Hong Kong, by means of any document, other than (a) to “professional investors” as defined in the Securities and Futures

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Ordinance (Cap. 571) of Hong Kong and any rules made under that Ordinance; or (b) in other circumstances which do not result in the document being a “prospectus” as defined in the Companies Ordinance (Cap. 32) of Hong Kong or which do not constitute an offer to the public within the meaning of that Ordinance. No advertisement, invitation or document relating to the shares of common stock has been or may be issued or has been or may be in the possession of any person for the purposes of issue, whether in Hong Kong or elsewhere, which is directed at, or the contents of which are likely to be accessed or read by, the public of Hong Kong (except if permitted to do so under the securities laws of Hong Kong) other than with respect to shares of common stock which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” as defined in the Securities and Futures Ordinance and any rules made under that Ordinance.

Japan

The shares of common stock have not been and will not be registered under the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948, as amended) and, accordingly, will not be offered or sold, directly or indirectly, in Japan, or for the benefit of any Japanese Person or to others for re-offering or resale, directly or indirectly, in Japan or to any Japanese Person, except in compliance with all applicable laws, regulations and ministerial guidelines promulgated by relevant Japanese governmental or regulatory authorities in effect at the relevant time. For the purposes of this paragraph, “Japanese Person” shall mean any person resident in Japan, including any corporation or other entity organized under the laws of Japan.

Korea

The shares of common stock have not been and will not be registered under the Financial Investments Services and Capital Markets Act of Korea and the decrees and regulations thereunder (the “FSCMA”), and the shares of common stock have been and will be offered in Korea as a private placement under the FSCMA. None of the shares of common stock may be offered, sold or delivered directly or indirectly, or offered or sold to any person for re-offering or resale, directly or indirectly, in Korea or to any resident of Korea except pursuant to the applicable laws and regulations of Korea, including the FSCMA and the Foreign Exchange Transaction Law of Korea and the decrees and regulations thereunder (the “FETL”). Furthermore, the purchaser of the shares of common stock shall comply with all applicable regulatory requirements (including but not limited to requirements under the FETL) in connection with the purchase of the shares of common stock. By the purchase of the shares of common stock, the relevant holder thereof will be deemed to represent and warrant that if it is in Korea or is a resident of Korea, it purchased the shares of common stock pursuant to the applicable laws and regulations of Korea.

Malaysia

No prospectus or other offering material or document in connection with the offer and sale of the shares of common stock has been or will be registered with the Securities Commission of Malaysia (“Commission”) for the Commission’s approval pursuant to the Capital Markets and Services Act 2007. Accordingly, this prospectus supplement and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the shares of common stock may not be circulated or distributed, nor may the shares of common stock be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Malaysia other than (i) a closed end fund approved by the Commission; (ii) a holder of a Capital Markets Services Licence; (iii) a person who acquires the shares of common stock, as principal, if the offer is on terms that the shares of common stock may only be acquired at a consideration of not less than RM250,000 (or its equivalent in foreign currencies) for each transaction; (iv) an individual whose total net personal assets or total net joint assets with his or her spouse exceeds RM3 million (or its equivalent in foreign currencies), excluding the value of the primary residence of the individual; (v) an individual who has a gross annual income exceeding RM300,000 (or its equivalent in foreign currencies) per annum in the preceding twelve months; (vi) an individual who, jointly with his or her spouse, has a gross annual income of RM400,000 (or its

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equivalent in foreign currencies), per annum in the preceding twelve months; (vii) a corporation with total net assets exceeding RM10 million (or its equivalent in a foreign currencies) based on the last audited accounts; (viii) a partnership with total net assets exceeding RM10 million (or its equivalent in foreign currencies); (ix) a bank licensee or insurance licensee as defined in the Labuan Financial Services and Securities Act 2010; (x) an Islamic bank licensee or takaful licensee as defined in the Labuan Financial Services and Securities Act 2010; and (xi) any other person as may be specified by the Commission; provided that, in each of the preceding categories (i) to (xi), the distribution of the shares of common stock is made by a holder of a Capital Markets Services License who carries on the business of dealing in securities. The distribution in Malaysia of this prospectus supplement is subject to Malaysian laws. This prospectus supplement does not constitute and may not be used for the purpose of public offering or an issue, offer for subscription or purchase, invitation to subscribe for or purchase any securities requiring the registration of a prospectus with the Commission under the Capital Markets and Services Act 2007.

Saudi Arabia

This document may not be distributed in the Kingdom of Saudi Arabia except to such persons as are permitted under the Offers of Securities Regulations as issued by the board of the Saudi Arabian Capital Market Authority (“CMA”) pursuant to resolution number 2-11-2004 dated 4 October 2004 as amended by resolution number 1-28-2008, as amended (the “CMA Regulations”). The CMA does not make any representation as to the accuracy or completeness of this document and expressly disclaims any liability whatsoever for any loss arising from, or incurred in reliance upon, any part of this document. Prospective purchasers of the securities offered hereby should conduct their own due diligence on the accuracy of the information relating to the securities. If you do not understand the contents of this document, you should consult an authorized financial adviser.

Singapore

This prospectus supplement has not been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus supplement and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of shares of common stock may not be circulated or distributed, nor may the shares of common stock be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”), (ii) to a relevant person pursuant to Section 275(1), or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275, of the SFA, or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the shares of common stock are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

securities (as defined in Section 239(1) of the SFA) of that corporation or the beneficiaries’ rights and interest (howsoever described) in that trust shall not be transferred within six months after that corporation or that trust has acquired the shares of common stock pursuant to an offer made under Section 275 of the SFA except:

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South Africa

Due to restrictions under the securities laws of South Africa, the shares of common stock are not offered, and the offer shall not be transferred, sold, renounced or delivered, in South Africa or to a person with an address in South Africa, unless one or other of the following exemptions applies:

This prospectus supplement does not, nor is it intended to, constitute an “offer to the public” (as that term is defined in the South African Companies Act, 2008, or the SA Companies Act, and does not, nor is it intended to, constitute a prospectus prepared and registered under the SA Companies Act. This document is not an “offer to the public” and must not be acted on or relied on by persons who do not fall within Section 96(1)(a) of the SA Companies Act (such persons being referred to as “relevant persons”). Any investment or investment activity to which this document relates is available only to relevant persons and will be engaged in only with relevant persons.

Switzerland

The shares of common stock may not be publicly offered in Switzerland and will not be listed on the SIX Swiss Exchange (“SIX”) or on any other stock exchange or regulated trading facility in Switzerland. This document has been prepared without regard to the disclosure standards for issuance prospectuses under art. 652a or art. 1156 of the Swiss Code of Obligations or the disclosure standards for listing prospectuses under art. 27 ff. of the SIX Listing Rules or the listing rules of any other stock exchange or regulated trading facility in Switzerland. Neither this document nor any other offering or marketing material relating to the shares of common stock or the offering may be publicly distributed or otherwise made publicly available in Switzerland.

Neither this document nor any other offering or marketing material relating to the offering, us or the shares of common stock have been or will be filed with or approved by any Swiss regulatory authority. In particular, this document will not be filed with, and the offer of shares of common stock will not be supervised by, the Swiss Financial Market Supervisory Authority (FINMA), and the offer of shares of common stock has not been and will not be authorized under the Swiss Federal Act on Collective Investment Schemes (“CISA”). The investor protection afforded to acquirers of interests in collective investment schemes under the CISA does not extend to acquirers of shares of common stock.

Taiwan

The shares of common stock have not been and will not be registered with the Financial Supervisory Commission of Taiwan pursuant to relevant securities laws and regulations and may not be sold, issued or offered within Taiwan through a public offering or in circumstances which constitutes an offer within the

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meaning of the Securities and Exchange Act of Taiwan that requires a registration or approval of the Financial Supervisory Commission of Taiwan. No person or entity in Taiwan has been authorized to offer, sell, give advice regarding or otherwise intermediate the offering and sale of the shares of common stock in Taiwan.

United Arab Emirates

The shares of common stock have not been, and are not being, publicly offered, sold, promoted or advertised in the United Arab Emirates (including the Dubai International Financial Centre) other than in compliance with the laws of the United Arab Emirates (and the Dubai International Financial Centre) governing the issue, offering and sale of securities. Further, this prospectus supplement does not constitute a public offer of securities in the United Arab Emirates (including the Dubai International Financial Centre) and is not intended to be a public offer. This prospectus supplement has not been approved by or filed with the Central Bank of the United Arab Emirates, the Securities and Commodities Authority or the Dubai Financial Services Authority.

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WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports, proxy statements and other information with the SEC (File No. 1-9894). We also filed a registration statement on Form S-3, including exhibits, under the Securities Act, with respect to the securities offered by this prospectus supplement and the accompanying prospectus. This prospectus supplement does not contain all of the information included in the registration statement or the exhibits. You can find our public filings with the SEC on the internet at a web site maintained by the SEC located at www.sec.gov.

We are “incorporating by reference” specified documents that we file with the SEC, which means:

We incorporate by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, after the date of this prospectus supplement and before the end of the offering of the securities pursuant to this prospectus supplement:

Notwithstanding the foregoing, information furnished under Items 2.02 and 7.01 of any Current Report on Form 8-K, including the related exhibits under Item 9.01, is not incorporated by reference in this prospectus.

You may obtain copies of documents incorporated by reference in this prospectus, at no cost, by request directed to us at the following address or telephone number:

Alliant Energy Corporation

4902 North Biltmore Lane

Madison, Wisconsin 53718

Attention: James H. Gallegos

Senior Vice President,

General Counsel & Corporate Secretary

(608) 458-3311

You can also find these filings on our website at www.alliantenergy.com. However, we are not incorporating the information on our website other than these filings into this prospectus.

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LEGAL MATTERS

The validity of the common stock offered in this prospectus supplement and certain legal matters will be passed upon for us by Perkins Coie LLP and for the underwriters by Gibson, Dunn & Crutcher LLP.

EXPERTS

The consolidated financial statements, and the related financial statement schedules, incorporated in this prospectus by reference from Alliant Energy Corporation’s Annual Report on Form 10-K, and the effectiveness of Alliant Energy Corporation and subsidiaries’ internal control over financial reporting have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their reports, which are incorporated herein by reference. Such financial statements and financial statement schedules have been so incorporated in reliance upon the reports of such firm given upon their authority as experts in accounting and auditing.

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PROSPECTUS

Alliant Energy Corporation

Common Stock

Debt Securities

Warrants

Stock Purchase Contracts

and

Stock Purchase Units

We may offer and sell from time to time securities in one or more offerings in amounts, at prices and on terms determined at the time of the offering. This prospectus provides you with a general description of the securities we may offer.

We may offer and sell the following securities:

Each time securities are sold using this prospectus, we will provide one or more prospectus supplements containing specific information about the offering and the terms of the securities being sold, including the offering price. Each prospectus supplement may also add, update or change information contained in this prospectus. You should carefully read this prospectus and the prospectus supplement relating to the specific issue of securities, together with the documents we incorporate by reference, before you invest.

We may offer and sell these securities to or through underwriters, dealers or agents, or directly to investors, on a continuous or a delayed basis. The applicable prospectus supplement will provide the specific terms of the plan of distribution.

In addition, selling shareowners to be named in a prospectus supplement may offer and sell from time to time shares of our common stock in such amounts as set forth in a prospectus supplement. Unless otherwise set forth in a prospectus supplement, we will not receive any proceeds from the sale of shares of our common stock by any selling shareowners.

Our common stock is listed on the New York Stock Exchange under the symbol “LNT.”

Investing in our securities involves risk. See “Risk Factors” on page 4 of this prospectus and in any prospectus supplement or such other document we refer you to in any prospectus supplement for a discussion of certain risks that prospective investors should consider before investing in our securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is accurate or complete. Any representation to the contrary is a criminal offense.

This prospectus is dated December 15, 2017.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS

References in this prospectus to “we,” “us” and “our” refer to Alliant Energy Corporation, unless the context otherwise requires. References to “common stock” refer to our common stock, $0.01 par value per share, and the attached common share purchase rights.

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or the SEC, utilizing a “shelf” registration process. Under this shelf registration process, we may, from time to time, sell the securities or combinations of the securities described in this prospectus, and one or more of our shareowners may sell our common stock, in one or more offerings. This prospectus provides you with a general description of those securities. Each time we, or, under certain circumstances, our shareowners, offer securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. The prospectus supplement may also add, update or change information contained in this prospectus and may include other special considerations applicable to such offering of securities. If there is any inconsistency between the information in this prospectus and any prospectus supplement, you should rely on the information in the prospectus supplement. You should read this prospectus and any prospectus supplement together with the additional information described under the heading “Where You Can Find More Information.”

You should rely only on the information contained or incorporated by reference in this prospectus and in any prospectus supplement. “Incorporated by reference” means that we can disclose important information to you by referring you to another document filed separately with the SEC. We have not authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it.

This prospectus and any prospectus supplement or information incorporated by reference herein or therein contains summaries of certain agreements that we have filed as exhibits to various SEC filings, as well as certain agreements that we will enter into in connection with the offering of securities covered by any prospectus supplement. The descriptions of these agreements contained in this prospectus and any prospectus supplement or information incorporated by reference herein or therein do not purport to be complete and are subject to, or qualified in their entirety by reference to, the definitive agreements. Copies of the definitive agreements will be made available without charge to you by making a written or oral request to us. See “Where You Can Find More Information.”

We are not making offers to sell nor soliciting offers to buy, nor will we make an offer to sell nor solicit an offer to buy, securities in any jurisdiction where the offer or sale is not permitted.

You should assume that the information appearing in this prospectus and any supplement to this prospectus, or the information we file or previously filed with the SEC that we incorporate by reference in this prospectus or any prospectus supplement, is accurate only as of the respective dates of those documents in which the information is contained. Our business, financial condition, results of operations and prospects may have changed since those dates.

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FORWARD-LOOKING STATEMENTS

This prospectus, any prospectus supplement and the information incorporated by reference herein or therein contain forward-looking statements intended to qualify for the safe harbor from liability established by the Private Securities Litigation Reform Act of 1995. All statements, other than statements of historical fact, included in this prospectus or any prospectus supplement or incorporated by reference herein or therein, including statements regarding anticipated financial performance, business strategy and management’s plans and objectives for future operations, are forward-looking statements. These forward-looking statements can be identified as such because the statements generally include words such as “may,” “believe,” “expect,” “anticipate,” “plan,” “project,” “will,” “projections,” “estimate,” or other words of similar import. These forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from those expressed in, or implied by, these statements. Readers are cautioned not to place undue reliance on these forward-looking statements. All forward-looking statements included in this prospectus, any prospectus supplement or in a document incorporated by reference herein or therein speak only as of the date of this prospectus, the applicable prospectus supplement or the document incorporated by reference, as the case may be. Additional information concerning factors that could cause actual results to differ materially from those in the forward-looking statements is contained under “Risk Factors” on page 4 of this prospectus and other documents that we file from time to time with the SEC that are incorporated by reference into this prospectus and any prospectus supplement. Numerous important factors described in this prospectus, any prospectus supplement and/or any document incorporated by reference in this prospectus and/or any prospectus supplement could affect these statements and could cause actual results to differ materially from our expectations. We assume no obligation, and disclaim any duty, to update or revise publicly any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

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ALLIANT ENERGY CORPORATION

Alliant Energy Corporation is an energy-services provider that operates as a regulated investor-owned public utility holding company. Our primary focus is to provide regulated electricity and natural gas service to customers in the Midwest through our two public utility subsidiaries, Interstate Power and Light Company, or IPL, and Wisconsin Power and Light Company, or WPL. We also have non-regulated operations. Our utility business is engaged principally in:

We are a “holding company” under the Public Utility Holding Company Act of 2005 and are subject to regulation by the Federal Energy Regulatory Commission, or the FERC, under that Act.

Our principal executive offices are located at 4902 North Biltmore Lane, Madison, Wisconsin 53718, and our telephone number is (608) 458-3311.

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RISK FACTORS

Investing in our securities involves risk. You should carefully consider the specific risks discussed or incorporated by reference in the applicable prospectus supplement, together with all the other information contained in the prospectus supplement or incorporated by reference in this prospectus. You should also consider the risks and uncertainties discussed under the caption “Risk Factors” included in our Annual Report on Form 10-K for the year ended December 31, 2016, which is incorporated by reference in this prospectus, and which may be amended, supplemented or superseded from time to time by other reports we file with the SEC in the future.

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RATIO OF EARNINGS TO FIXED CHARGES

The following table shows our ratio of earnings to fixed charges for the periods presented:

USE OF PROCEEDS

Unless we inform you otherwise in the applicable prospectus supplement, we intend to use the net proceeds from the sale of the securities for general corporate purposes, which may include repayment or refinancing of debt, acquisitions, working capital, capital expenditures, investments and repurchases and redemptions of securities. Net proceeds may be temporarily invested prior to use.

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DESCRIPTION OF COMMON STOCK

The following description of our common stock summarizes material terms and provisions that apply to the common stock. The summary may not contain all of the information that is important to you and is subject to and qualified in its entirety by reference to our articles of incorporation, our bylaws and our rights agreement, which are filed as exhibits to the registration statement of which this prospectus is a part. See “Where You Can Find More Information.”

General

Our restated articles of incorporation, as amended, provide that we have authority to issue 480,000,000 shares of common stock, $0.01 par value per share. We do not have the authority under our restated articles of incorporation, as amended, to issue shares of preferred stock.

Common Stock

Holders of our common stock are entitled to such dividends as our board of directors may declare from time to time in accordance with applicable law. Our ability to pay dividends is dependent upon a number of factors, including the ability of our subsidiaries to pay dividends. Our utility subsidiaries each have restrictions on the payment of dividends on their common stock based on the regulatory restrictions applicable to them, and IPL has restrictions on the payment of dividends on its common stock based on the terms of its outstanding preferred stock.

Holders of our common stock will be entitled to vote for the election of members to our board of directors and on all other matters. Holders of our common stock are entitled to one vote per share of common stock held by them on all matters properly submitted to a vote of shareowners, subject to Section 180.1150 of the Wisconsin Business Corporation Law. See “—Statutory and Bylaw Provisions.” Shareowners have no cumulative voting rights, which means that the holders of shares entitled to exercise more than 50% of the voting power are able to elect all of the directors to be elected. Our board of directors is divided into three classes, with staggered terms of three years each.

All shares of common stock are entitled to participate equally in distributions in liquidation. Holders of common stock have no preemptive rights to subscribe for or purchase our shares. There are no conversion rights, sinking fund or redemption provisions applicable to our common stock.

Common Share Purchase Rights

We have entered into a rights agreement pursuant to which each outstanding share of our common stock has attached a right to purchase one-quarter of one share of our common stock. A right will also attach to each share of common stock that we subsequently issue prior to the expiration of the rights agreement. Under circumstances described below, the rights will entitle the holder of the rights to purchase additional shares of common stock. In this prospectus and any accompanying prospectus supplement, unless the context requires otherwise, all references to our common stock include the accompanying rights.

Currently, the rights are not exercisable and trade with the common stock. If the rights become exercisable, each full right, unless held by a person or group that beneficially owns more than 15% of our outstanding common stock, will initially entitle the holder to purchase one-quarter of one share of our common stock at a purchase price of $55 per full share, subject to adjustment. The rights will become exercisable only if a person or group has acquired, or announced an intention to acquire, 15% or more of our outstanding common stock. Under some circumstances, including the existence of a 15% acquiring party, each holder of a right, other than the acquiring party, will be entitled to purchase at the right’s then-current exercise price, shares of our common stock having a market value of two times the exercise price. If another corporation acquires us after a party acquires

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15% or more of our common stock, each holder of a right will be entitled to receive the acquiring corporation’s common shares having a market value of two times the exercise price. The rights may be redeemed at a price of $0.001 per right until a party acquires 15% or more of our common stock and, after that time, may be exchanged for one share of our common stock per right until a party acquires 50% or more of our common stock. The rights expire on December 11, 2018, subject to extension. Under the rights agreement, our board of directors may reduce the thresholds applicable to the rights from 15% to not less than 10%. The rights do not have voting or dividend rights and, until they become exercisable, have no dilutive effect on our earnings.

The rights have certain anti-takeover effects, in that they could have the effect of delaying, deferring or preventing a change of control of our company by causing substantial dilution to a person or group that attempts to acquire a significant interest in our company on terms not approved by our board of directors.

Statutory and Bylaw Provisions

Provisions of Wisconsin law and our amended and restated bylaws might also discourage some types of transactions that involve an actual or threatened change of control of our company.

Section 196.795(3) of the Wisconsin Statutes provides that no person may take, hold or acquire, directly or indirectly, more than 10% of the outstanding voting securities of a public utility holding company, such as us, without the approval of the Public Service Commission of Wisconsin, or the PSCW.

Section 180.1150 of the Wisconsin Business Corporation Law provides that the voting power of shares of public Wisconsin corporations, such as us, held by any person or persons acting as a group in excess of 20% of the corporation’s voting power is limited to 10% of the full voting power of those shares, unless full voting power of those shares has been restored pursuant to a vote of shareowners. Sections 180.1140 to 180.1144 of the Wisconsin Business Corporation Law contain some limitations and special voting provisions applicable to specified business combinations involving Wisconsin corporations, such as us, and a significant shareowner, unless the board of directors of the corporation approves either the business combination or the purchase of shares that causes the shareowner to become a significant shareowner before such purchase occurs.

Similarly, Sections 180.1130 to 180.1133 of the Wisconsin Business Corporation Law contain special voting provisions applicable to some business combinations, unless specified minimum price and procedural requirements are met. Following commencement of a takeover offer, Section 180.1134 of the Wisconsin Business Corporation Law imposes special voting requirements on share repurchases effected at a premium to the market and on asset sales by the corporation, unless, as it relates to the potential sale of assets, the corporation has at least three independent directors and a majority of the independent directors vote not to have the provision apply to the corporation.

In addition, our amended and restated bylaws establish a procedure that shareowners seeking to call a special meeting of shareowners must satisfy. This procedure involves notice to us, the receipt by us of written demands for a special meeting from holders of 10% or more of the issued and outstanding shares of common stock, a review of the validity of such demands by an independent inspector appointed by us and the fixing of the record and meeting dates by our board of directors. In addition, shareowners demanding such a special meeting must deliver to us a written agreement to pay the costs incurred by us in holding a special meeting, including the costs of preparing and mailing the proxy materials for our solicitation of proxies for use at such meeting, in the event such shareowners are unsuccessful in their proxy solicitation.

Our amended and restated bylaws also provide our board of directors with discretion in postponing shareowner meetings, including, within certain limits, special meetings of shareowners. Additionally, our chairman or board of directors (acting by resolution) may adjourn a shareowner meeting at any time prior to the transaction of business at such meeting, within certain limits. Our amended and restated bylaws also contain strict time deadlines and procedures applicable to shareowners seeking to nominate a person for election as a director or to otherwise bring business before a meeting.

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DESCRIPTION OF DEBT SECURITIES

The following description of the debt securities, or notes, sets forth certain material terms and provisions of the notes to which any prospectus supplement may relate. The following description does not purport to be complete and is subject to, and is qualified in its entirety by reference to, the indenture between us and Wells Fargo Bank, National Association, as trustee, dated September 30, 2009, as it may be supplemented and amended from time to time. The indenture is an exhibit to the registration statement of which this prospectus is a part. The terms of the notes will include those stated in the indenture and those made a part of the indenture by reference to the Trust Indenture Act of 1939, as amended, which we refer to as the 1939 Act.

The particular terms of the notes offered by any prospectus supplement and the extent, if any, to which the provisions described in this prospectus may apply to the offered notes will be described in the prospectus supplement relating to the offered notes. Accordingly, for a description of the terms of a particular issue of notes, reference must be made to both the prospectus supplement relating thereto and to the following description.

The notes will be issued as unsecured debt securities under the indenture and will rank equally with all of our other unsecured and unsubordinated debt. The notes will be effectively subordinated to all of our secured debt. The indenture does not limit the aggregate principal amount of notes that may be issued under the indenture and provides that notes may be issued from time to time in one or more series pursuant to the terms of one or more supplemental indentures, board resolutions or officer’s certificates pursuant to a supplemental indenture or a board resolution. The indenture gives us the ability to reopen a previous issue of notes and issue additional notes of such series, unless otherwise provided.

Provisions of a Particular Series

The prospectus supplement applicable to each series of notes will specify, among other things:

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The indenture does not contain provisions that afford holders of notes protection in the event of a highly leveraged transaction involving us.

Some of the notes may be issued as original issue discount notes. Such notes are sold at a discount below their stated principal amount. If we issue these securities, the prospectus supplement will describe any special tax, accounting or other information which we think is important. We encourage you to consult with your own tax and financial advisors on these important matters.

Registration and Transfer

We will not be required to (i) issue, register the transfer of or exchange notes of any series during a period of 15 days immediately preceding the date notice is given identifying the notes of such series called for redemption, or (ii) issue, register the transfer of or exchange any notes so selected for redemption, in whole or in part, except the unredeemed portion of any note being redeemed in part.

Payment and Paying Agent

Unless otherwise indicated in an applicable prospectus supplement, payment of principal of any notes will be made only against surrender to the paying agent of such notes. Principal of and interest on notes will be payable, subject to any applicable laws and regulations, at the office of such paying agent or paying agents as we may designate from time to time. Payment of interest on notes on any interest payment date will be made to the person in whose name the notes (or predecessor security) are registered at the close of business on the record date for such interest payment.

Unless otherwise indicated in an applicable prospectus supplement, the trustee will act as paying agent with respect to the notes. We may at any time designate additional paying agents or rescind the designation of any paying agents or approve a change in the office through which any paying agent acts.

All moneys paid by us to a paying agent for the payment of the principal of (and premium, if any) or interest on the notes of any series which remain unclaimed at the end of two years after such principal or interest shall have become due and payable will be repaid to us, upon request and subject to applicable abandoned property laws, and the holder of such notes will from that time forward look only to us for payment of such principal, premium and interest.

Limitation on Liens

Unless otherwise specified in a prospectus supplement for notes of a particular series, the following covenant will apply to the notes of that series.

So long as any notes remain outstanding, we will not secure any indebtedness with a lien on any shares of the capital stock of any of our significant subsidiaries, which shares of capital stock we directly or indirectly own from the date of the indenture or thereafter, unless we equally and ratably secure all notes. However, this restriction does not apply to or prevent:

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Liens on any shares of the capital stock of any of our significant subsidiaries to secure any indebtedness, other than liens described in (1) and (2) above, are referred to in this prospectus as “restricted liens.” The foregoing limitations do not apply to the extent that we create any restricted liens to secure indebtedness that, together with all of our other indebtedness secured by restricted liens, does not at the time exceed 10% of our consolidated net tangible assets, as determined by us as of a month end not more than 90 days prior to the closing or consummation of the proposed transaction.

For this purpose, “indebtedness” applied to any person means (i) any liability of such person (A) for borrowed money, or under any reimbursement obligation relating to a letter of credit (other than trade letters of credit) issued to support indebtedness or obligations of such person or others of the kinds referred to in this definition, or (B) evidenced by a bond, note, debenture or similar instrument, or (C) for payment obligations arising under any conditional sale or other title retention arrangement (including a purchase money obligation) given in connection with the acquisition of any businesses, properties or assets of any kind, or (D) for the payment of money relating to a capitalized lease obligation; (ii) any liability of others described in the preceding clause (i) that such person has guaranteed or that is otherwise its legal liability; and (iii) any amendment, supplement, modification, deferral, renewal, extension or refunding of any liability of the types referred to in clauses (i) and (ii) above.

For this purpose, “consolidated net tangible assets” means the total amount of our assets determined on a consolidated basis in accordance with generally accepted accounting principles, or GAAP, less (i) the sum of our consolidated current liabilities determined in accordance with GAAP and (ii) the amount of our consolidated assets classified as intangible assets determined in accordance with GAAP, including but not limited to, such items as goodwill, trademarks, trade names, patents, and unamortized debt discount and expense and regulatory assets carried as an asset on our consolidated balance sheet.

For this purpose, “significant subsidiary” means any direct, majority owned subsidiary of us that is a “significant subsidiary” as defined in Regulation S-X promulgated by the SEC.

Regulations prohibit or restrict the encumbrance or pledge of public utility assets for the benefit of an associated company. Any pledge of WPL’s common stock to secure the notes could require approval of the FERC or the PSCW. Any pledge of IPL’s common stock to secure the notes could require approval of the FERC. Even with a valid pledge of IPL’s or WPL’s common stock, foreclosure under the indenture may be subject to applicable regulatory requirements, including approval by each of the FERC or the PSCW, if foreclosure or the sale of the pledged IPL or WPL common stock may constitute a transfer of control of IPL or WPL. Applicable law gives each of the FERC and the PSCW broad discretion to define “control” for these purposes, and any such determination would depend upon the facts and circumstances existing at the time. Accordingly, the ability to foreclose on and dispose of IPL or WPL common stock may be restricted or delayed by applicable regulatory requirements.

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Consolidation, Merger and Sale

We may not consolidate with or merge into any other corporation or convey, transfer or lease our properties and assets substantially as an entirety to any person, unless:

Notwithstanding the foregoing, we may merge or consolidate with or transfer all or substantially all of our assets to an affiliate that has no significant assets or liabilities and was formed solely for the purpose of changing our jurisdiction of organization or our form of organization; provided that the amount of our indebtedness is not increased; and provided, further that the successor assumes all of our obligations under the indenture.

Modification

The indenture contains provisions permitting us and the trustee, with the consent of the holders of not less than a majority in aggregate principal amount of the outstanding notes of each series that is affected, to modify the indenture or the rights of the holders of the notes of such series; provided that no such modification may, without the consent of the holder of each outstanding note that is affected:

In addition, we and the trustee may execute, without the consent of any holders of notes, any supplemental indenture for certain other customary purposes, including the creation of any new series of notes.

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Events of Default

The indenture provides that any one or more of the following described events with respect to the notes of any series, which has occurred and is continuing, constitutes an “event of default” with respect to the notes of such series:

The holders of not less than a majority in aggregate outstanding principal amount of the notes of any series have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee with respect to the notes of such series. If an event of default occurs and is continuing with respect to the notes of any series, then the trustee or the holders of not less than 33% in aggregate outstanding principal amount of the notes of such series may declare the principal amount of the notes due and payable immediately by notice in writing to us (and to the trustee if given by the holders), and upon any such declaration such principal amount shall become immediately due and payable. At any time after such a declaration of acceleration with respect to the notes of any series has been made and before a judgment or decree for payment of the money due has been obtained as provided in the indenture, the holders of not less than a majority in aggregate outstanding principal amount of the notes of such series may rescind and annul such declaration and its consequences if the default has been cured or waived and we have paid or deposited with the trustee a sum sufficient to pay all matured installments of interest and principal (and premium, if any) due otherwise than by acceleration and all sums paid or advanced by the trustee, including reasonable compensation and expenses of the trustee.

The holders of not less than a majority in aggregate outstanding principal amount of the notes of any series, on behalf of the holders of all the notes of such series, may waive any past default with respect to such series, except (i) a default in the payment of principal (or premium, if any) or interest or (ii) a default in respect of a covenant or provision which as provided under the indenture cannot be modified or amended without the consent of the holder of each outstanding note of such series affected.

Satisfaction and Discharge

We will be discharged from our obligations on the notes of any series, or any portion of the principal amount of the notes of any series, if we irrevocably deposit with the trustee or any paying agent (other than us) sufficient cash or eligible obligations (or a combination of both) to pay the principal, or portion of principal, premium, if any, and interest, if any, due and to become due, and deliver to the trustee or such paying agent:

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For this purpose, “eligible obligations” for U.S. dollar-denominated notes, means securities that are direct obligations of, or obligations the full and timely payment of which are unconditionally guaranteed by, the United States, entitled to the benefit of the full faith and credit thereof, or depository receipts issued by a bank as custodian with respect to these obligations or any specific interest, principal or other payments due in respect thereof held by the custodian in accordance with the indenture for the account of the holder of a depository receipt.

In the event that all of the conditions set forth above have been satisfied for any series of notes, or portions thereof, except that, for any reason, we have not delivered the officer’s certificate and opinion of counsel described in the second and third bulleted items above, the holders of those notes will no longer be entitled to the benefits of certain of our covenants under the indenture, including the covenant described above in “—Limitation on Liens.” Our indebtedness under those notes, however, will not be deemed to have been satisfied and discharged prior to maturity, and the holders of those notes may continue to look to us for payment of the indebtedness represented by those notes.

The indenture will be deemed satisfied and discharged when no notes remain outstanding and we have paid all other sums payable by us under the indenture and delivered an officer’s certificate and opinion of counsel to the trustee stating that the conditions to satisfaction and discharge contained in the indenture have been met. All moneys we pay to the trustee or any paying agent on notes (or hold in trust for payment thereof) which remain unclaimed at the end of two years after payments have become due will be paid to us (or, discharged if so held in trust) upon request, subject to certain notice provisions and applicable abandoned property laws. Thereafter, the holder of those notes may look only to us for payment and not the trustee or any paying agent.

Information Concerning the Trustee

The trustee, prior to an event of default with respect to notes of any series, undertakes to perform, with respect to notes of such series, only such duties as are specifically set forth in the indenture and, in case an event of default with respect to notes of any series has occurred and is continuing, shall exercise, with respect to notes of such series, such of the rights and powers vested in it by the indenture, and use the same degree of care and skill as a prudent individual would exercise in the conduct of his or her own affairs. Subject to such provision, the trustee is under no obligation to exercise any of the powers vested in it by the indenture at the request of any holder of notes of any series, unless offered reasonable security and indemnity by such holder against the costs, expenses and liabilities which might be incurred by the trustee. The trustee is not required to expend or risk its own funds or otherwise incur any financial liability in the performance of its duties if the trustee reasonably believes that repayment or adequate indemnity is not reasonably assured to it. The trustee may decline to follow any such direction from a holder if, among other reasons, the trustee determines in good faith that the actions or proceedings as directed may not lawfully be taken, would involve the trustee in personal liability or would be unduly prejudicial to the holders of the notes of such series not joining in such direction.

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Pursuant to the 1939 Act, if a default occurs with respect to notes of any series, the trustee may be required to resign as trustee under the indenture if it has a conflicting interest (as defined in the 1939 Act), unless the default is cured, duly waived or otherwise eliminated within 90 days.

We and certain of our subsidiaries may maintain deposit accounts and banking relationships with the trustee. The trustee and certain of its affiliates may also serve as trustee under other indentures pursuant to which our securities and certain of our subsidiaries are outstanding.

Governing Law

The indenture and the notes will be governed by, and construed in accordance with, the internal laws of the State of New York.

Global Securities

We will issue the notes in whole or in part in the form of one or more global certificates, which we refer to as global securities. We will deposit the global securities with or on behalf of The Depository Trust Company, which we refer to as DTC, and registered in the name of Cede & Co., as nominee of DTC. Beneficial interests in the global securities may be held through the Euroclear System (“Euroclear”) and Clearstream Banking, S.A. (“Clearstream”) (as indirect participants in DTC).

We have provided the following descriptions of the operations and procedures of DTC, Euroclear and Clearstream solely as a matter of convenience. These operations and procedures are solely within the control of DTC, Euroclear and Clearstream and are subject to change by them from time to time. Neither we, any underwriter nor the trustee take any responsibility for these operations or procedures, and you are urged to contact DTC, Euroclear or Clearstream directly to discuss these matters.

DTC has advised us that:

We expect that under procedures established by DTC:

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Investors in the global securities who are participants in DTC’s system may hold their interests therein directly through DTC. Investors in the global securities who are not participants may hold their interests therein indirectly through organizations (including Euroclear and Clearstream) which are participants in such system. Euroclear and Clearstream may hold interests in the global securities on behalf of their participants through customers’ securities accounts in their respective names on the books of their respective depositories, which are Euroclear Bank S.A./N.V., as operator of Euroclear, and Citibank, N.A., as depository of Clearstream. All interests in the global securities, including those held through Euroclear or Clearstream, may be subject to the procedures and requirements of DTC. Those interests held through Euroclear or Clearstream may also be subject to the procedures and requirements of such systems.

The laws of some jurisdictions require that purchasers of securities take physical delivery of those securities in the form of a certificate. For that reason, it may not be possible to transfer interests in a global security to those persons. In addition, because DTC can act only on behalf of its participants, who in turn act on behalf of persons who hold interests through participants, the ability of a person having an interest in a global security to pledge or transfer that interest to persons or entities that do not participate in DTC’s system, or otherwise to take actions in respect of that interest, may be affected by the lack of a physical definitive security in respect of that interest.

So long as DTC or its nominee is the registered owner of a global security, DTC or that nominee will be considered the sole owner or holder of the notes represented by that global security for all purposes under the applicable indenture and under the notes. Except as described below, owners of beneficial interests in a global security will not be entitled to have notes represented by that global security registered in their names, will not receive or be entitled to receive the notes in the form of a physical certificate and will not be considered the owners or holders of the notes under the applicable indenture or under the notes, and may not be entitled to give the trustee directions, instructions or approvals. For that reason, each holder owning a beneficial interest in a global security must rely on DTC’s procedures and, if that holder is not a direct or indirect participant in DTC, on the procedures of the DTC participant through which that holder owns its interest, to exercise any rights of a holder of notes under the applicable indenture or the global security.

Neither we nor the trustee will have any responsibility or liability for any aspect of DTC’s records relating to the notes or relating to payments made by DTC on account of the notes, or any responsibility to maintain, supervise or review any of DTC’s records relating to the notes.

We will make payments (including principal, premium, if any, and interest) on the notes represented by the global securities to DTC or its nominee, as the registered owner of the notes, by wire transfer of immediately available funds to the accounts specified by the registered owner of the notes. We expect that when DTC or its nominee receives any payment on the notes represented by a global security, DTC will credit participants’ accounts with payments in amounts proportionate to their beneficial interests in the global security as shown in DTC’s records. We also expect that payments by DTC’s participants to owners of beneficial interests in the global security held through those participants will be governed by standing instructions and customary practice as is now the case with securities held for the accounts of customers registered in the names of nominees for such customers. DTC’s participants will be responsible for those payments.

DTC has advised us that it will take any action permitted to be taken by a holder of notes only at the direction of one or more participants to whose account DTC has credited the interests in the global securities and only in respect of such portion of the aggregate principal amount of the notes as to which such participant or participants has or have given such direction. However, if there is an event of default under the notes, DTC reserves the right to exchange the global securities for certificated securities, and to distribute such securities to its participants.

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Initial settlement for the notes will be made in immediately available funds. Transfers between participants in DTC will be effected in accordance with DTC’s procedures, and transfers between participants in Euroclear and Clearstream will be effected in accordance with their respective rules and operating procedures. The notes represented by the global securities are expected to be eligible to trade in DTC’s Same-Day Funds Settlement System, and any permitted secondary market trading activity in such notes will, therefore, be required by DTC to be settled in immediately available funds.

Cross-market transfers between the participants in DTC, on the one hand, and Euroclear or Clearstream participants, on the other hand, will be effected through DTC in accordance with DTC’s rules on behalf of Euroclear or Clearstream, as the case may be, by its depository; however, such cross-market transactions will require delivery of instructions to Euroclear or Clearstream, as the case may be, by the counterparty in such system in accordance with the rules and procedures and within the established deadlines (European time) of such system. Euroclear or Clearstream, as the case may be, will, if the transaction meets its settlement requirements, deliver instructions to its respective depository to take action to effect final settlement on its behalf by delivering or receiving interests in the relevant global security in DTC, and making or receiving payment in accordance with normal procedures for same-day funds settlement applicable to DTC. Euroclear participants and Clearstream participants may not deliver instructions directly to the depositories for Euroclear or Clearstream.

Because of time zone differences, the securities account of a Euroclear or Clearstream participant purchasing an interest in a global security from a participant in DTC will be credited, and any such crediting will be reported to the relevant Euroclear or Clearstream participant, during the securities settlement processing day (which must be a business day for Euroclear and Clearstream) immediately following the settlement date of DTC. DTC has advised us that cash received in Euroclear or Clearstream as a result of sales of interests in a global securities by or through a Euroclear or Clearstream participant to a participant in DTC will be received with value on the settlement date of DTC but will be available in the relevant Euroclear or Clearstream cash account only as of the business day for Euroclear or Clearstream following DTC’s settlement date.

Although DTC, Euroclear and Clearstream have agreed to the foregoing procedures to facilitate transfers of interests in the global securities among participants in DTC, Euroclear and Clearstream, they are under no obligation to perform or to continue to perform such procedures, and may discontinue such procedures at any time. Neither we nor the trustee nor any of our or their respective agents will have any responsibility for the performance by DTC, Euroclear or Clearstream or their respective direct or indirect participants of their respective obligations under the rules and procedures governing their operations.

Certificated Notes

We will issue certificated notes to each person that DTC identifies as the beneficial owner of notes represented by the global securities upon surrender by DTC of the global securities only if:

Neither we nor the trustee will be liable for any delay by DTC, its nominee or any direct or indirect participant in identifying the beneficial owners of the related notes. We and the trustee may conclusively rely on, and will be protected in relying on, instructions from DTC or its nominee, including instructions about the registration and delivery, and the respective principal amounts, of the notes to be issued.

We will make all payments of principal, interest and premium, if any, with respect to certificated notes by wire transfer of immediately available funds to the accounts specified by the holders of the certificated notes or, if no such account is specified, by mailing a check to each such holder’s registered address. We expect that secondary trading in any certificated notes will also be settled in immediately available funds.

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DESCRIPTION OF WARRANTS

The following summary of certain provisions of the warrants does not purport to be complete and is subject to, and is qualified in its entirety by reference to, all provisions of the applicable warrant agreement.

We may issue warrants for the purchase of debt securities, common stock or other securities. Warrants may be issued independently or together with debt securities, common stock or other securities offered by any prospectus supplement and may be attached to or separate from any such offered securities. Each series of warrants will be issued under a separate warrant agreement to be entered into between us and a bank or trust company, as warrant agent, all as will be set forth in the prospectus supplement relating to the particular issue of warrants. The warrant agent will act solely as our agent in connection with the warrants and will not assume any obligation or relationship of agency or trust for or with any holders of warrants or beneficial owners of warrants.

Reference is made to the prospectus supplement relating to the particular issue of warrants offered pursuant to such prospectus supplement for the terms of and information relating to such warrants, including, where applicable:

Warrants will be issued in registered form only. The exercise price for warrants will be subject to adjustment in accordance with provisions described in the applicable prospectus supplement.

Each warrant will entitle the holder thereof to purchase such principal amount of debt securities or such number of shares of common stock or other securities at such exercise price as will in each case be set forth in, or calculable from, the prospectus supplement relating to the warrants, which exercise price may be subject to adjustment upon the occurrence of certain events as set forth in such prospectus supplement. After the close of business on the expiration date, or such later date to which such expiration date may be extended by us, unexercised warrants will become void. The place or places where, and the manner in which, warrants may be exercised will be specified in the prospectus supplement.

Prior to the exercise of any warrants to purchase debt securities, common stock or other securities, holders of such warrants will not have any of the rights of holders of debt securities, common stock or other securities, as the case may be, purchasable upon such exercise, including the right to receive payments of principal of, premium, if any, or interest, if any, on the debt securities purchasable upon such exercise or to enforce covenants in the applicable indenture, or to receive payments of dividends, if any, on the common stock purchasable upon such exercise, or to exercise any applicable right to vote.

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DESCRIPTION OF STOCK PURCHASE CONTRACTS AND STOCK PURCHASE UNITS

The following summary of certain provisions of the stock purchase contracts and stock purchase units does not purport to be complete and is subject to, and is qualified in its entirety by reference to, all provisions of the applicable stock purchase contracts or stock purchase units.

We may issue stock purchase contracts, including contracts obligating holders to purchase from us, and obligating us to sell to the holders, a specified number of shares of common stock or other securities at a future date or dates. The price per security and the number of securities may be fixed at the time the stock purchase contracts are issued or may be determined by reference to a specific formula set forth in the stock purchase contracts. The stock purchase contracts may be issued separately or as part of stock purchase units consisting of a stock purchase contract and debt securities, warrants, other securities or debt obligations of third parties, including U.S. treasury securities, securing the holders’ obligations to purchase the securities under the stock purchase contracts. The stock purchase contracts may require holders to secure their obligations under the stock purchase contracts in a specified manner. The stock purchase contracts also may require us to make periodic payments to the holders of the stock purchase units or vice versa, and those payments may be unsecured or refunded on some basis.

The stock purchase contracts, and, if applicable, collateral or depositary arrangements relating to the stock purchase contracts or stock purchase units, will be filed with the SEC in connection with the offering of stock purchase contracts or stock purchase units. The prospectus supplement relating to a particular issue of stock purchase contracts or stock purchase units will describe the terms of those stock purchase contracts or stock purchase units, including the following:

If we issue stock purchase units where debt obligations of third parties are used as security for your obligations to purchase or sell shares of common stock or other securities, we will include in the prospectus supplement relating to the offering information about the issuer of the debt obligations. Specifically, if the issuer has a class of securities registered under the Exchange Act and is either eligible to register its securities on Form S-3 under the Securities Act of 1933, as amended, or the Securities Act, or meets the listing criteria to be listed on a national securities exchange, we will include a brief description of the business of the issuer, the market price of its securities and how you can obtain more information about the issuer. If the issuer does not meet the criteria described in the previous sentence, we will include substantially all of the information that would be required if the issuer were making a public offering of the debt obligations.

SELLING SHAREOWNERS

We may register shares of common stock covered by this prospectus for re-offers and resales by any selling shareowners to be named in a prospectus supplement. We may register these shares to permit selling shareowners to resell their shares when they deem appropriate. A selling shareowner may resell all, a portion or none of such shareowner’s shares at any time and from time to time. Selling shareowners may also sell, transfer or otherwise dispose of some or all of their shares of our common stock in transactions exempt from the registration requirements of the Securities Act. We do not know when or in what amounts the selling shareowners may offer shares for sale under this prospectus and any prospectus supplement. We will not receive any proceeds from any sale of shares by a selling shareowner under this prospectus and any prospectus supplement. We may pay all expenses incurred with respect to the registration of the shares of common stock owned by the selling shareowners, other than underwriting fees, discounts or commissions which will be borne by the selling shareowners. We will provide you with a prospectus supplement naming the selling shareowners, the amount of shares to be registered and sold and any other terms of the shares of common stock being sold by each selling shareowner.

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PLAN OF DISTRIBUTION

We may sell our securities, and any selling shareowner may sell shares of our common stock, in any one or more of the following ways from time to time: (1) through agents; (2) to or through underwriters; (3) through brokers or dealers; (4) in “at the market offerings” within the meaning of Rule 415(a)(4) under the Securities Act, to or through a market maker or into an existing trading market, on an exchange or otherwise; (5) directly by us or any selling shareowners to purchasers, including through a specific bidding, auction or other process; or (6) through a combination of any of these methods of sale. The applicable prospectus supplement will contain the terms of the transaction, name or names of any underwriters, dealers, agents and the respective amounts of securities underwritten or purchased by them, the initial public offering price of the securities, and the applicable agent’s commission, dealer’s purchase price or underwriter’s discount. Any selling shareowners, dealers and agents participating in the distribution of the securities may be deemed to be underwriters, and compensation received by them on resale of the securities may be deemed to be underwriting discounts. Additionally, because selling shareowners may be deemed to be “underwriters” within the meaning of Section 2(11) of the Securities Act, selling shareowners may be subject to the prospectus delivery requirements of the Securities Act.

Any initial offering price, dealer purchase price, discount or commission may be changed from time to time.

The securities may be distributed from time to time in one or more transactions, at negotiated prices, at a fixed price or fixed prices (that may be subject to change), at market prices prevailing at the time of sale, at various prices determined at the time of sale or at prices related to prevailing market prices.

Offers to purchase securities may be solicited directly by us or any selling shareowner or by agents designated by us from time to time. Unless otherwise indicated in the prospectus supplement, any such agent will use its commercially reasonable efforts to solicit purchases for the period of its appointment or to sell securities on a continuing basis. Agents may receive compensation in the form of commissions, discounts or concessions from us. Agents may also receive compensation from the purchasers of the securities for whom they sell as principals. Each particular agent will receive compensation in amounts negotiated in connection with the sale, which might be in excess of customary commissions. Any such agent may be deemed to be an underwriter, as that term is defined in the Securities Act, of the securities so offered and sold. Accordingly, any commission, discount or concession received by them and any profit on the resale of the securities purchased by them may be deemed to be underwriting discounts or commissions under the Securities Act. We have not entered into any agreements, understandings or arrangements with any underwriters or broker-dealers regarding the sale of their securities. As of the date of this prospectus, there are no special selling arrangements between any broker-dealer or other person and us. No period of time has been fixed within which the securities will be offered and sold.

If underwriters are utilized in the sale of any securities in respect of which this prospectus is being delivered, such securities will be acquired by the underwriters for their own account and may be resold from time to time in one or more transactions, including negotiated transactions, at fixed public offering prices or at varying prices determined by the underwriters at the time of sale. Securities may be offered to the public either through underwriting syndicates represented by managing underwriters or directly by one or more underwriters. If any underwriter or underwriters are utilized in the sale of securities, unless otherwise indicated in the applicable prospectus supplement, the obligations of the underwriters are subject to certain conditions precedent, and the underwriters will be obligated to purchase all such securities if they purchase any of them.

If a dealer is utilized in the sale of the securities in respect of which this prospectus is delivered, we will sell such securities, and any selling shareowner will sell shares of our common stock to the dealer, as principal. The dealer may then resell such securities to the public at varying prices to be determined by such dealer at the time of resale. Transactions through brokers or dealers may include block trades in which brokers or dealers will attempt to sell shares as agent but may position and resell as principal to facilitate the transaction or in cross trades, in which the same broker or dealer acts as agent on both sides of the trade. Any such dealer may be deemed to be an underwriter, as such term is defined in the Securities Act, of the securities so offered and sold.

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In addition, any selling shareowner may sell shares of our common stock in ordinary brokerage transactions or in transactions in which a broker solicits purchases.

Offers to purchase securities may be solicited directly by us or any selling shareowner, and the sale thereof may be made by us or any selling shareowner, directly to institutional investors or others who may be deemed to be underwriters within the meaning of the Securities Act with respect to any resale thereof.

Agents, underwriters and dealers may be entitled under relevant agreements with us or any selling shareowner to indemnification by us against certain liabilities, including liabilities under the Securities Act, or to contribution with respect to payments which such agents, underwriters and dealers may be required to make in respect thereof. The terms and conditions of any indemnification or contribution will be described in the applicable prospectus supplement.

We may pay all expenses incurred with respect to the registration of the shares of common stock owned by any selling shareowners, other than underwriting fees, discounts or commissions, which will be borne by the selling shareowners. We or any selling shareowner may also sell shares of our common stock through various arrangements involving mandatorily or optionally exchangeable securities, and this prospectus may be delivered in connection with those sales.

We or any selling shareowner may enter into derivative, sale or forward sale transactions with third parties, or sell securities not covered by this prospectus to third parties in privately negotiated transactions. If the applicable prospectus supplement indicates, in connection with those transactions, the third parties may sell securities covered by this prospectus and the applicable prospectus supplement, including in short sale transactions and by issuing securities not covered by this prospectus but convertible into, exchangeable for or representing beneficial interests in securities covered by this prospectus, or the return of which is derived in whole or in part from the value of such securities. The third parties may use securities received under derivative, sale or forward sale transactions or securities pledged by us or any selling shareowner or borrowed from us, any selling shareowner or others to settle those sales or to close out any related open borrowings of stock, and may use securities received from us or any selling shareowner in settlement of those transactions to close out any related open borrowings of stock. The third party in such sale transactions will be an underwriter and will be identified in the applicable prospectus supplement.

Additionally, certain selling shareowners may engage in hedging transactions with broker-dealers in connection with distributions of shares or otherwise. In those transactions, broker-dealers may engage in short sales of shares in the course of hedging the positions they assume with such selling shareowner. Certain selling shareowners also may sell shares short and redeliver shares to close out such short positions. Certain selling shareowners may also enter into option or other transactions with broker-dealers which require the delivery of shares to the broker-dealer. The broker-dealer may then resell or otherwise transfer such shares pursuant to this prospectus. Certain selling shareowners also may loan or pledge shares, and the borrower or pledgee may sell or otherwise transfer the shares so loaned or pledged pursuant to this prospectus. Such borrower or pledgee also may transfer those shares to investors in our securities or the selling shareowner’s securities or in connection with the offering of other securities not covered by this prospectus.

Underwriters, broker-dealers or agents may receive compensation in the form of commissions, discounts or concessions from us or any selling shareowner. Underwriters, broker-dealers or agents may also receive compensation from the purchasers of shares for whom they act as agents or to whom they sell as principals, or both. Compensation as to a particular underwriter, broker-dealer or agent will be in amounts to be negotiated in connection with transactions involving shares and might be in excess of customary commissions. In effecting sales, broker-dealers engaged by us or any selling shareowner may arrange for other broker-dealers to participate in the resales.

Any securities offered other than common stock will be a new issue and, other than the common stock, which is listed on the New York Stock Exchange, will have no established trading market. We may elect to list

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any series of securities on an exchange, and in the case of the common stock, on any additional exchange, but, unless otherwise specified in the applicable prospectus supplement and/or other offering material, we shall not be obligated to do so. No assurance can be given as to the liquidity of the trading market for any of the securities.

Agents, underwriters and dealers may engage in transactions with, or perform services for, us or our subsidiaries or any selling shareowner in the ordinary course of business.

Any underwriter may engage in overallotment, stabilizing transactions, short covering transactions and penalty bids in accordance with Regulation M under the Exchange Act. Overallotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Short covering transactions involve purchases of the securities in the open market after the distribution is completed to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time. An underwriter may carry out these transactions on the New York Stock Exchange, in the over-the-counter market or otherwise.

The place and time of delivery for securities will be set forth in the accompanying prospectus supplement.

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports, proxy statements and other information with the SEC (File No. 1-9894). We also filed a registration statement on Form S-3, including exhibits, under the Securities Act, with respect to the securities offered by this prospectus. This prospectus is a part of the registration statement, but does not contain all of the information included in the registration statement or the exhibits. You may read and copy the registration statement and any other document that we file with the SEC at the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. You can call the SEC at 1-800-SEC-0330 for further information on the operation of the Public Reference Room. You can also find our public filings with the SEC on the internet at a web site maintained by the SEC located at http://www.sec.gov.

We are “incorporating by reference” specified documents that we file with the SEC, which means:

We incorporate by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, after the date of this prospectus and before the end of the offering of the securities pursuant to this prospectus:

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Notwithstanding the foregoing, information furnished under Items 2.02 and 7.01 of any Current Report on Form 8-K, including the related exhibits under Item 9.01, is not incorporated by reference in this prospectus.

You may obtain copies of documents incorporated by reference in this prospectus, at no cost, by request directed to us at the following address or telephone number:

Alliant Energy Corporation

4902 North Biltmore Lane

Madison, Wisconsin 53718

Attention: James H. Gallegos, Senior Vice

President, General Counsel and Corporate

Secretary

(608) 458-3311

You can also find these filings on our website at www.alliantenergy.com. However, we are not incorporating the information on our website other than these filings into this prospectus.

Any statement contained herein or in a document incorporated or deemed to be incorporated by reference herein will be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained herein, in any other subsequently filed document which also is or is deemed to be incorporated by reference herein or in any prospectus supplement, modifies or supersedes such statement. Any such statement so modified or superseded will not be deemed, except as so modified and superseded, to constitute a part of this prospectus.

LEGAL MATTERS

Unless otherwise specified in a prospectus supplement accompanying this prospectus, the validity of the securities offered in this prospectus and certain legal matters will be passed upon for us by Perkins Coie LLP. If the securities are being distributed in an underwritten offering, certain legal matters will be passed upon for the underwriters by counsel identified in the related prospectus supplement.

EXPERTS

The consolidated financial statements, and the related financial statement schedules, incorporated in this prospectus by reference from Alliant Energy Corporation’s 2016 Annual Report on Form 10-K, and the effectiveness of Alliant Energy Corporation and subsidiaries’ internal control over financial reporting have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their reports, which are incorporated herein by reference. Such financial statements and financial statement schedules have been so incorporated in reliance upon the reports of such firm given upon their authority as experts in accounting and auditing.

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$326,000,000

Alliant Energy Corporation

Common Stock

PROSPECTUS SUPPLEMENT

Goldman Sachs & Co. LLC

BofA Merrill Lynch

December     , 2018