FORM 6-K

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Report of Foreign Private Issuer

Pursuant to Rule 13a-16 or 15d-16

of the Securities Exchange Act of 1934

For the month of October, 2018

Commission File Number: 001-09531

Telefónica, S.A.

(Translation of registrant’s name into English)

Distrito Telefónica, Ronda de la Comunicación s/n,

28050 Madrid, Spain

3491-482 87 00

(Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

Form 20-F   ☒             Form 40-F  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):

Yes  ☐             No  ☒

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):

Yes  ☐             No  ☒

Indicate by check mark whether by furnishing the information contained in this Form, the registrant is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934:

Yes  ☐             No  ☒

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): N/A

Telefónica, S.A.

TABLE OF CONTENTS

FINANCIAL HIGHLIGHTS

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Comments from José María Álvarez-Pallete, Executive Chairman:

“Third quarter results reflect the solid execution of our strategic priorities. To begin with, both high-value customers and their average revenue continued increasing, with a strong level of net additions in mobile contract (including the best figure for Spain over the last ten years), LTE, fibre and Pay TV. More and higher-value customers, coupled with stable churn rates, translates into higher business sustainability. If we add to that the wider coverage of our high-speed networks, the efficiencies we are already achieving in digitalisation and simplification, and the launch of Movistar Home via AURA, among others, we are further strengthening our future positioning.

Additionally, revenues and operating cash flow accelerated their organic annual growth, free cash flow reached 3 billion euros, up 0.9% versus the previous year excluding spectrum, and net debt decreased for the sixth straight quarter.

Improved growth trends, robust and solid business third quarter and our good operating positioning in key markets allow us to upgrade our revenue growth guidance set for 2018.”

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TELEFÓNICA

SELECTED FINANCIAL DATA

Unaudited figures (Euros in millions)

Notes:

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DISCLAIMER

This document may contain forward-looking statements and information (hereinafter, the “Statements”) relating to the Telefónica Group (hereinafter, the “Company” or “Telefónica”) or otherwise. These Statements may include financial forecasts and estimates based on assumptions or statements regarding plans, objectives and expectations that make reference to different matters, such as the customer base and its evolution, growth of the different business lines and of the global business, market share, possible acquisitions, divestitures or other transactions, Company’s results and other aspects related to the activity and situation of the Company.

The Statements can be identified, in certain cases, through the use of words such as “forecast”, “expectation”, “anticipation”, “aspiration”, “purpose”, “belief” or similar expressions or variations of such expressions. These Statements reflect the current views of Telefónica with respect to future events, do not represent, by their own nature, any guarantee of future fulfilment, and are subject to risks and uncertainties that could cause the final developments and results to materially differ from those expressed or implied by such Statements. These risks and uncertainties include those identified in the documents containing more comprehensive information filed by Telefónica before the different supervisory authorities of the securities markets in which its shares are listed and, in particular, the Spanish National Securities Market Commission.

Except as required by applicable law, Telefónica does not assume any obligation to publicly update the Statements to adapt them to events or circumstances taking place after the date hereof, including changes in the Company’s business, in its business development strategy or any other unexpected circumstance.

This document may contain summarized, non-audited or non-GAAP financial information. The information contained herein should therefore be considered as a whole and in conjunction with all the public information regarding the Company available, including, if any, other documents released by the Company that may contain more detailed information.

In October 2015, the European Securities Markets Authority (ESMA) published guidelines on Alternative Performance Measures (APM), applicable to regulated information published from July 3, 2016. Information related to APM used in the present document are included in the Appendix “Alternative performance measures”, page 46 of this document. Moreover, recipients of this document are invited to read our condensed consolidated interim financial statements and consolidated interim management report for the six-month period ended Jun 30, 2018 submitted to the Spanish National Securities Market Commission (CNMV), in Note 2, page 13, of the pdf filed.

Neither this document nor any of its contents constitute an offer to purchase, sale or exchange any security, a solicitation of any offer to purchase, sale or exchange any security, or a recommendation or advice regarding any security.

For further information please refer to the information on 2018 third quarter financial results filed by the Company and also available on the Company’s website: www.telefonica.com

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.