EXHIBIT 32.1

                            CERTIFICATION PURSUANT TO
            SECTION 1350, CHAPTER 63 OF TITLE 18, UNITED STATES CODE,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

      Pursuant to Section 1350, Chapter 63 of Title 18, United States Code, as
adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, the
undersigned, as Chief Executive Officer of Forrester Research, Inc. (the
"Company"), does hereby certify that to the undersigned's knowledge:

      1)    the Company's Annual Report on Form 10-K for the year ended December
            31, 2005 fully complies with the requirements of Section 13(a) or
            15(d) of the Securities Exchange Act of 1934; and

      2)    the information contained in the Company's Annual Report on
            Form 10-K for the year ended December 31, 2005 fairly presents, in
            all material respects, the financial condition and results of
            operations of the Company.

                 /s/ George F. Colony
                 --------------------
                 George F. Colony
                 Chairman of the Board of Directors and Chief
                 Executive Officer

Dated: March 14, 2006