SCHEDULE 14(A)

(Rule 14a-101)

Information Required in Proxy Statement

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the Securities

Exchange Act of 1934 (Amendment No.     )

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☐ Preliminary Proxy Statement

☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☐ Definitive Proxy Statement

☑ Definitive Additional Materials

☐ Soliciting Material Pursuant to § 240.14a-12

FORRESTER RESEARCH, INC.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

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Your Vote Counts! FORRESTER RESEARCH, INC. ATTN: RYAN D. DARRAH 60 ACORN PARK DRIVE CAMBRIDGE, MA 02140 FORRESTER RESEARCH, INC. 2021 Annual Meeting Vote by May 10, 2021 11:59 PM EDT You invested in FORRESTER RESEARCH, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy materials for the shareholder meeting to be held on May 11, 2021. Vote Virtually at the Meeting* May 11, 2021 10:00 AM EDT Virtually at: www.virtualshareholdermeeting.com/FORR2021 *Many shareholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. Smartphone users Point your camera here and vote without entering a control number V1 For complete information and to vote, visit www.ProxyVote.com Control # D40822-P49749 Get informed before you vote View the Proxy Statement and Annual Report online OR you can receive a free paper or email copy of the material(s) by requesting prior to April 27, 2021. If you would like to request a copy of the material(s) for this and/or future shareholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to sendmaterial@proxyvote.com. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy.

THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming shareholder meeting. Please follow the instructions on the reverse side to vote on these important matters. Vote at www.ProxyVote.com Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Sign up for E-delivery”. Voting Items Board Recommends D40823-P49749 1. Election of Directors Nominees: 2. To ratify the selection of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting firm for fiscal 2021. 3. To approve, by non-binding vote, executive compensation. NOTE: Such other business as may properly come before the meeting or any adjournment thereof. For For For 01) Jean M. Birch 02) David Boyce 03) Neil Bradford 04) George F. Colony 05) Anthony Friscia 06) Robert M. Galford 07) Gretchen Teichgraeber 08) Yvonne Wassenaar