EXHIBIT 21 SUBSIDIARIES OF THE REGISTRANT Whitcomb Investments, Inc., a Massachusetts corporation Forrester Research, B.V., a Dutch corporation. Forrester Research Limited, a United Kingdom corporation Forrester Research KK, a Japanese corporation Forrester Research Australia Pty. Ltd., an Australian corporation Forrester Research (Canada) Inc., a Canadian corporation Forrester Research GmbH & Co. KG, a German partnership Forrester Verwaltungs GmbH, a German corporation Forrester Beteiligungs GmbH, a German corporation Forrester Research GmbH, a Swiss corporation Forrester Research Israel Limited, an Israeli corporation Forrester Research SAS, a French corporation Forrester Research APS, a Danish corporation Forrester Research S.r.l., an Italian corporation Giga Information Group Limited, a United Kingdom corporation Whitcomb AB, a Swedish corporation