UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): February 1, 2017

CEB Inc.

(Exact Name Of Registrant As Specified In Its Charter)

Registrant’s Telephone Number, Including Area Code: (571) 303-3000

N/A

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Item 8.01. Other Events

On January 5, 2017, CEB Inc. (the “Company”) announced that they have entered into a definitive agreement whereby Gartner, Inc. (“Gartner”) will acquire all of the outstanding shares of the Company in a cash and stock transaction valued at approximately $2.6 billion. Gartner will also assume (and refinance) approximately $0.9 billion in the Company debt. Closing of the transaction is subject to the approval of the Company’s shareholders and the satisfaction of customary closing conditions, including applicable regulatory approvals. On February 1, 2017, the Federal Trade Commission granted early termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the “HSR Act”), applicable to the proposed transaction. Closing of the transaction is expected to be completed in the first half of 2017. Additional information, including the press release announcing the proposed transaction, can be obtained at the Company’s Investor Relations site at www.cebglobal.com.

Additional Information and Where to Find It

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities, or a solicitation of any vote or approval, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction.

This communication is being made in respect of a proposed business combination involving Gartner and the Company. In connection with the proposed transaction, Gartner will file with the Securities and Exchange Commission (the “SEC”) a Registration Statement on Form S-4 that includes the preliminary proxy statement of the Company and that will also constitute a prospectus of Gartner. The information in the preliminary proxy statement/prospectus is not complete and may be changed. Gartner may not issue the common stock referenced in the proxy statement/prospectus until the Registration Statement on Form S-4 filed with the SEC becomes effective. The preliminary proxy statement/prospectus, this Current Report on Form 8-K and any related communication are not offers to sell Gartner securities, are not soliciting an offer to buy Gartner securities in any state where the offer and sale is not permitted and are not a solicitation of any vote or approval. The definitive proxy statement/prospectus will be mailed to stockholders of the Company.

GARTNER AND THE COMPANY URGE INVESTORS AND SECURITY HOLDERS TO READ THE DEFINITIVE PROXY STATEMENT/PROSPECTUS AND OTHER DOCUMENTS FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION.

Investors and security holders will be able to obtain these materials (when they are available) and other documents filed with the SEC free of charge at the SEC’s website, www.sec.gov. Copies of documents filed with the SEC by Gartner (when they become available) may be obtained free of charge on Gartner’s website at www.gartner.com or by directing a written request to Gartner, Inc., Investor Relations, 56 Top Gallant Road Stamford, CT 06902-7747. Copies of documents filed with the SEC by the Company (when they become available) may be obtained free of charge on the Company’s website at www.cebglobal.com or by directing a written request to the Company care of Investor Relations, 1919 North Lynn Street, Arlington, VA 22209.

Participants in the Merger Solicitation

Each of Gartner, the Company and their respective directors, executive officers and certain other members of management and employees may be deemed to be participants in the solicitation of proxies in respect of the proposed transaction. Information regarding these persons who may, under the rules of the SEC, be considered participants in the solicitation of the Company’s stockholders in connection with the proposed transaction is set forth in the proxy statement/prospectus described above filed with the SEC. Additional information regarding Gartner’s executive officers and directors is included in Gartner’s definitive proxy statement, which was filed with the SEC on April 11, 2016. Additional information regarding the Company’s executive officers and directors is included in the Company’s definitive proxy statement, which was filed with the SEC on April 29, 2016. You can obtain free copies of these documents using the information in the paragraph immediately above.

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 hereunto duly authorized.