EXHIBIT 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in the Registration
Statements on Form S-8 (Nos. 333-16905, 333-22749, 333-96393, 333-38626,
333-99749, and 333-99751) of Forrester Research, Inc. of our reports dated March
14, 2006, relating to the consolidated financial statements and the
effectiveness of internal control over financial reporting of Forrester
Research, Inc., which appear in this Form 10-K.

/s/ BDO Seidman, LLP

Boston, Massachusetts
March 14, 2006