content: <PAGE>   1
  
      As filed with the Securities and Exchange Commission on February 8, 2000
  
                                                          File No. 333-___________
  ================================================================================
  
                         SECURITIES AND EXCHANGE COMMISSION
                               WASHINGTON, D.C. 20549
  
                                      FORM S-8
  
                               REGISTRATION STATEMENT
  
                                        UNDER
  
                             THE SECURITIES ACT OF 1933
  
                              FORRESTER RESEARCH, INC.
               (Exact name of registrant as specified in its charter)
  
              DELAWARE                                             04-2797789
    (State or other jurisdiction                                (I.R.S. Employer
  of incorporation or organization)                            Identification No.)
  
                                400 Technology Square
                           Cambridge, Massachusetts 02139
                                   (617) 497-7090
            (Address of principal executive offices, including zip code)
  
                    AMENDED AND RESTATED FORRESTER RESEARCH, INC.
                             1996 EQUITY INCENTIVE PLAN
  
                             ------------------------
                             (Full title of the plan)
  
                                SUSAN M. WHIRTY, ESQ.
                     Chief Financial Officer and General Counsel
                              Forrester Research, Inc.
                                400 Technology Square
                           Cambridge, Massachusetts 02139
                                   (617) 497-7090
                                (617) 868-0577 (Fax)
  
                           ------------------------------
   (Name, Address and Telephone Number, including Area Code, of Agent for Service)
  
                           CALCULATION OF REGISTRATION FEE
  <TABLE>
  <CAPTION>
  ====================================================================================================================
   Title of Securities        Amount to be         Proposed maximum          Proposed maximum        Amount of
   to be registered           registered           offering price            aggregate offering      registration fee
                                                   per share(1)              price(2)
  --------------------------------------------------------------------------------------------------------------------
  <S>                         <C>                    <C>                         <C>                     <C>
  Common Stock,
  par value $.01              5,000,000 shares       $0.81 - $34.155             $90,392,514             $23,864
  ====================================================================================================================
  </TABLE>
  
  (1)  The offering price for shares subject to options on the date hereof is the
       actual exercise price of such options. Of the 5,000,000 shares to be
       registered hereunder, 89,258 shares are subject to options at an exercise
       price of $0.81 per share, 2,519,090 shares are subject to options at an
       exercise price of $11.69 per share, 3,000 shares are subject to options at
       an exercise price of $11.94 per share, 10,000 shares are subject to options
       at an exercise price of $12.855 per share, 6,000 shares are subject to
       options at an exercise price of $12.875 per share, 10,000 shares are
       subject to options at an exercise price of $14.065 per share, 6,000 shares
       are subject to options at an exercise price of $15.045 per share, 6,000
       shares are subject to options at an exercise price of $15.235 per share,
       15,000 shares are subject to options at an exercise price of $16.155 per
       share, 7,000 shares are subject to options at an exercise price of $16.44
       per share, 12,000 shares are subject to options at an exercise price of
       $16.625 per share, 15,000 shares are subject to options at an exercise
       price of $17.00 per share, 12,000 shares are subject to options at an
       exercise price of $17.815 per share, 6,000 shares are subject to options at
       an exercise price of $18.095 per share, 20,000 shares are subject to
       options at an exercise price of $18.28 per share, 3,000 shares are subject
       to options at an exercise price of $19.25 per share, 10,000 shares are
       subject to options at an exercise price of $19.565 per share, 10,000 shares
       are subject to options at an exercise price of $19.875 per share, 128,000
       shares are subject to options at an exercise price of $20.065 per share,
       3,000 shares are subject to options at an exercise price of $20.53 per
       share, 50,000 shares are subject to options at an exercise price of $21.47
       per share, 10,000 shares are subject to options at an exercise price of
       $22.72 per share, 30,000 shares are subject to options at an exercise price
       of $23.065
  
  
  <PAGE>   2
  
  
       per share, 10,000 shares are subject to options at an exercise price of
       $23.345 per share, 281,998 shares are subject to options at an exercise
       price of $23.94 per share, 725,600 shares are subject to options at an
       exercise price of $24.64 per share, 206,000 shares are subject to options
       at an exercise price of $28.47 per share, 8,000 shares are subject to
       options at an exercise price of $30.69 per share, 15,000 shares are subject
       to options at an exercise price of $33.875 per share and 18,000 shares are
       subject to options at an exercise price of $34.155 per share. The offering
       price for the remaining 755,054 shares not subject to options on the date
       hereof of $28.66 per share has been estimated solely for the purpose of
       determining the registration fee pursuant to Rule 457(h) on the basis of
       the average of the high and low prices of Forrester Research, Inc. Common
       Stock, par value $0.01 per share, reported on the Nasdaq National Market on
       February 1, 2000.
  
  (2)  The maximum aggregate offering price consists of $72,298.98 payable in
       respect of 89,258 shares subject to options at an exercise price of $0.81
       per share, plus $29,448,162.10 payable in respect of 2,519,090 shares
       subject to options at an exercise price of $11.69 per share, plus $35,820
       payable in respect of 3,000 shares subject to options at an exercise price
       of $11.94 per share, plus $128,550 payable in respect of 10,000 shares
       subject to options at an exercise price of $12.855 per share, plus $77,250
       payable in respect of 6,000 shares subject to options at an exercise price
       of $12.875 per share, plus $140,650 payable in respect of 10,000 shares
       subject to options at an exercise price of $14.065 per share, plus $90,270
       payable in respect of 6,000 shares subject to options at an exercise price
       of $15.045 per share, plus $91,410 payable in respect of 6,000 shares
       subject to options at an exercise price of $15.235 per share, plus $242,325
       payable in respect of 15,000 shares subject to options at an exercise price
       of $16.155 per share, plus $115,080 payable in respect of 7,000 shares
       subject to options at an exercise price of $16.44 per share, plus $199,500
       payable in respect of 12,000 shares subject to options at an exercise price
       of $16.625 per share, plus $255,000 payable in respect of 15,000 shares
       subject to options at an exercise price of $17.00 per share, plus $213,780
       payable in respect of 12,000 shares subject to options at an exercise price
       of $17.815 per share, plus $108,570 payable in respect of 6,000 shares
       subject to options at an exercise price of $18.095 per share, plus $365,600
       payable in respect of 20,000 shares subject to options at an exercise price
       of $18.28 per share, plus $57,750 payable in respect of 3,000 shares
       subject to options at an exercise price of $19.25 per share, plus $195,650
       payable in respect of 10,000 shares subject to options at an exercise price
       of $19.565 per share, plus $198,750 payable in respect of 10,000 shares
       subject to options at an exercise price of $19.875 per share, plus
       $2,568,320 payable in respect of 128,000 shares subject to options at an
       exercise price of $20.065 per share, plus $61,590 payable in respect of
       3,000 shares subject to options at an exercise price of $20.53 per share,
       plus $1,073,500 payable in respect of 50,000 shares subject to options at
       an exercise price of $21.47 per share, plus $227,200 payable in respect of
       10,000 shares subject to options at an exercise price of $22.72 per share,
       plus $691,950 payable in respect of 30,000 shares subject to options at an
       exercise price of $23.065 per share, plus $233,450 payable in respect of
       10,000 shares subject to options at an exercise price of $23.345 per share,
       plus $6,751,032.12 payable in respect of 281,998 shares subject to options
       at an exercise price of $23.94 per share, plus $17,878,784 payable in
       respect of 725,600 shares subject to options at an exercise price of $24.64
       per share, plus $5,864,820 payable in respect of 206,000 shares subject to
       options at an exercise price of $28.47 per share, plus $245,520 payable in
       respect of 8,000 shares subject to options at an exercise price of $30.69
       per share, plus $508,125 payable in respect of 15,000 shares subject to
       options at an exercise price of $33.875 per share, plus $614,790 payable in
       respect of 18,000 shares subject to options at an exercise price of $34.155
       per share, plus $21,637,016.19 payable in respect of 755,054 shares that
       have not yet been subject to options on the date hereof.
  
  ================================================================================
  
  
                                        -2-
  <PAGE>   3
  
  
                                  EXPLANATORY NOTE
  
       This Registration Statement has been filed pursuant to General Instruction
  E on Form S-8, to register 5,000,000 additional securities to be offered
  pursuant to the Amended and Restated Forrester Research, Inc. 1996 Equity
  Incentive Plan (the "1996 Plan") of Forrester Research, Inc. (the "Registrant"
  or the "Company"). A registration statement on Form S-8 (No. 333-22749), filed
  with the Commission on March 4, 1997 to register 2,900,000 shares of common
  stock offered pursuant to the 1996 Plan and the 1996 Stock Option Plan for
  Non-Employee Directors is currently effective and is hereby incorporated herein
  by reference.
  
       All share numbers and per share information in this Registration Statement
  are adjusted to give effect to the two-for-one stock split paid on February 7,
  2000.
  
  
                                        -3-
  <PAGE>   4
  
  
                                     SIGNATURES
  
       Pursuant to the requirements of the Securities Act of 1933, the Registrant
  certifies that it has reasonable grounds to believe that it meets all of the
  requirements for filing on Form S-8 and has duly caused this Registration
  Statement on Form S-8 to be signed on its behalf by the undersigned, thereunto
  duly authorized, in the City of Cambridge, The Commonwealth of Massachusetts, on
  this 8th day of February, 2000.
  
                                             FORRESTER RESEARCH, INC.
  
  
                                             By: /s/ Susan M. Whirty
                                                 ---------------------------------
                                                 Name:  Susan M. Whirty
                                                 Title: Chief Financial Officer,
                                                        Vice President, Operations
                                                        and General Counsel
  
                                  POWER OF ATTORNEY
                                  -----------------
  
       Pursuant to the requirement of the Securities Act of 1933, this
  Registration Statement has been signed by the following persons in the
  capacities and on the dates indicated. Each person whose signature appears below
  hereby authorizes and constitutes George F. Colony and Susan M. Whirty, with
  full power of substitution, to execute in the name of and on behalf of such
  person any amendment (including any post-effective amendment) to this
  Registration Statement, and any subsequent registration statement for the same
  offering that may be filed under Rule 462(b) under the Securities Act, and to
  file the same, with exhibits thereto, and other documents in connection
  therewith, making such changes in this Registration Statement and any subsequent
  registration statement under Rule 462(b) as the person(s) so acting deems
  appropriate.
  
  <TABLE>
  <CAPTION>
  Signature                                Title                                            Date
  ---------                                -----                                            ----
  
  <S>                                      <C>                                              <C>
  /s/ George F. Colony                     President, Chief Executive                       February 8, 2000
  ----------------------                   Officer and Chairman of the Board
  George F. Colony
  
  /s/ Susan M. Whirty                      Chief Financial Officer and                      February 8, 2000
  ----------------------                   General Counsel (Principal
  Susan M. Whirty                          Financial and Accounting Officer)
  
  /s/ Robert M. Galford                    Director                                         February 8, 2000
  ----------------------
  Robert M. Galford
  </TABLE>
  
  
                                        -4-
  <PAGE>   5
  
  
  <TABLE>
  <CAPTION>
  <S>                                      <C>                                              <C>
  /s/ George R. Hornig                     Director                                         February 8, 2000
  ----------------------
  George R. Hornig
  
  /s/ Michael H. Welles                    Director                                         February 8, 2000
  ----------------------
  Michael H. Welles
  
  /s/ Henk W. Broeders                     Director                                         February 8, 2000
  ----------------------
  Henk W. Broeders
  </TABLE>
  
  
                                        -5-
  <PAGE>   6
  
  
                                    EXHIBIT INDEX
  
  <TABLE>
  <CAPTION>
  Number                         Title of Exhibit                                       Page
  ------                         ----------------                                       ----
  <S>                            <C>                                                     <C>
   5                             Opinion of Ropes & Gray
  
  23.1                           Consent of Arthur Andersen LLP
  
  23.2                           Consent of Ropes & Gray (contained in the
                                 opinion filed as Exhibit 5 hereto)
  
  24.                            Power of Attorney (included as part of the
                                 signature page filed herewith)
  </TABLE>
  
  
                                        -6-
metadata_documents: [{"type": "S-8", "sequence": "1", "description": "FORRESTER RESEARCH, INC.", "secsgml_size_bytes": 15161}]
metadata_filer: {"company-data": {"conformed-name": "FORRESTER RESEARCH INC", "cik": "0001023313", "assigned-sic": "8700", "irs-number": "042797789", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-96393", "film-number": "527293"}, "business-address": {"street1": "400 TECHNOLOGY SQUARE", "city": "CAMBRIDGE", "state": "MA", "zip": "02139", "phone": "6174977090"}, "mail-address": {"street1": "400 TECHNOLOGY SQUARE", "city": "CAMBRIDGE", "state": "MA", "zip": "02139"}}
text: 1
  
      As filed with the Securities and Exchange Commission on February 8, 2000
  
                                                          File No. 333-___________
  ================================================================================
  
                         SECURITIES AND EXCHANGE COMMISSION
                               WASHINGTON, D.C. 20549
  
                                      FORM S-8
  
                               REGISTRATION STATEMENT
  
                                        UNDER
  
                             THE SECURITIES ACT OF 1933
  
                              FORRESTER RESEARCH, INC.
               (Exact name of registrant as specified in its charter)
  
              DELAWARE                                             04-2797789
    (State or other jurisdiction                                (I.R.S. Employer
  of incorporation or organization)                            Identification No.)
  
                                400 Technology Square
                           Cambridge, Massachusetts 02139
                                   (617) 497-7090
            (Address of principal executive offices, including zip code)
  
                    AMENDED AND RESTATED FORRESTER RESEARCH, INC.
                             1996 EQUITY INCENTIVE PLAN
  
                             ------------------------
                             (Full title of the plan)
  
                                SUSAN M. WHIRTY, ESQ.
                     Chief Financial Officer and General Counsel
                              Forrester Research, Inc.
                                400 Technology Square
                           Cambridge, Massachusetts 02139
                                   (617) 497-7090
                                (617) 868-0577 (Fax)
  
                           ------------------------------
   (Name, Address and Telephone Number, including Area Code, of Agent for Service)
  
                           CALCULATION OF REGISTRATION FEE
  ====================================================================================================================
   Title of Securities        Amount to be         Proposed maximum          Proposed maximum        Amount of
   to be registered           registered           offering price            aggregate offering      registration fee
                                                   per share(1)              price(2)
  --------------------------------------------------------------------------------------------------------------------
  Common Stock,
  par value $.01              5,000,000 shares       $0.81 - $34.155             $90,392,514             $23,864
  ====================================================================================================================
  (1)  The offering price for shares subject to options on the date hereof is the
       actual exercise price of such options. Of the 5,000,000 shares to be
       registered hereunder, 89,258 shares are subject to options at an exercise
       price of $0.81 per share, 2,519,090 shares are subject to options at an
       exercise price of $11.69 per share, 3,000 shares are subject to options at
       an exercise price of $11.94 per share, 10,000 shares are subject to options
       at an exercise price of $12.855 per share, 6,000 shares are subject to
       options at an exercise price of $12.875 per share, 10,000 shares are
       subject to options at an exercise price of $14.065 per share, 6,000 shares
       are subject to options at an exercise price of $15.045 per share, 6,000
       shares are subject to options at an exercise price of $15.235 per share,
       15,000 shares are subject to options at an exercise price of $16.155 per
       share, 7,000 shares are subject to options at an exercise price of $16.44
       per share, 12,000 shares are subject to options at an exercise price of
       $16.625 per share, 15,000 shares are subject to options at an exercise
       price of $17.00 per share, 12,000 shares are subject to options at an
       exercise price of $17.815 per share, 6,000 shares are subject to options at
       an exercise price of $18.095 per share, 20,000 shares are subject to
       options at an exercise price of $18.28 per share, 3,000 shares are subject
       to options at an exercise price of $19.25 per share, 10,000 shares are
       subject to options at an exercise price of $19.565 per share, 10,000 shares
       are subject to options at an exercise price of $19.875 per share, 128,000
       shares are subject to options at an exercise price of $20.065 per share,
       3,000 shares are subject to options at an exercise price of $20.53 per
       share, 50,000 shares are subject to options at an exercise price of $21.47
       per share, 10,000 shares are subject to options at an exercise price of
       $22.72 per share, 30,000 shares are subject to options at an exercise price
       of $23.065
  2
  
       per share, 10,000 shares are subject to options at an exercise price of
       $23.345 per share, 281,998 shares are subject to options at an exercise
       price of $23.94 per share, 725,600 shares are subject to options at an
       exercise price of $24.64 per share, 206,000 shares are subject to options
       at an exercise price of $28.47 per share, 8,000 shares are subject to
       options at an exercise price of $30.69 per share, 15,000 shares are subject
       to options at an exercise price of $33.875 per share and 18,000 shares are
       subject to options at an exercise price of $34.155 per share. The offering
       price for the remaining 755,054 shares not subject to options on the date
       hereof of $28.66 per share has been estimated solely for the purpose of
       determining the registration fee pursuant to Rule 457(h) on the basis of
       the average of the high and low prices of Forrester Research, Inc. Common
       Stock, par value $0.01 per share, reported on the Nasdaq National Market on
       February 1, 2000.
  
  (2)  The maximum aggregate offering price consists of $72,298.98 payable in
       respect of 89,258 shares subject to options at an exercise price of $0.81
       per share, plus $29,448,162.10 payable in respect of 2,519,090 shares
       subject to options at an exercise price of $11.69 per share, plus $35,820
       payable in respect of 3,000 shares subject to options at an exercise price
       of $11.94 per share, plus $128,550 payable in respect of 10,000 shares
       subject to options at an exercise price of $12.855 per share, plus $77,250
       payable in respect of 6,000 shares subject to options at an exercise price
       of $12.875 per share, plus $140,650 payable in respect of 10,000 shares
       subject to options at an exercise price of $14.065 per share, plus $90,270
       payable in respect of 6,000 shares subject to options at an exercise price
       of $15.045 per share, plus $91,410 payable in respect of 6,000 shares
       subject to options at an exercise price of $15.235 per share, plus $242,325
       payable in respect of 15,000 shares subject to options at an exercise price
       of $16.155 per share, plus $115,080 payable in respect of 7,000 shares
       subject to options at an exercise price of $16.44 per share, plus $199,500
       payable in respect of 12,000 shares subject to options at an exercise price
       of $16.625 per share, plus $255,000 payable in respect of 15,000 shares
       subject to options at an exercise price of $17.00 per share, plus $213,780
       payable in respect of 12,000 shares subject to options at an exercise price
       of $17.815 per share, plus $108,570 payable in respect of 6,000 shares
       subject to options at an exercise price of $18.095 per share, plus $365,600
       payable in respect of 20,000 shares subject to options at an exercise price
       of $18.28 per share, plus $57,750 payable in respect of 3,000 shares
       subject to options at an exercise price of $19.25 per share, plus $195,650
       payable in respect of 10,000 shares subject to options at an exercise price
       of $19.565 per share, plus $198,750 payable in respect of 10,000 shares
       subject to options at an exercise price of $19.875 per share, plus
       $2,568,320 payable in respect of 128,000 shares subject to options at an
       exercise price of $20.065 per share, plus $61,590 payable in respect of
       3,000 shares subject to options at an exercise price of $20.53 per share,
       plus $1,073,500 payable in respect of 50,000 shares subject to options at
       an exercise price of $21.47 per share, plus $227,200 payable in respect of
       10,000 shares subject to options at an exercise price of $22.72 per share,
       plus $691,950 payable in respect of 30,000 shares subject to options at an
       exercise price of $23.065 per share, plus $233,450 payable in respect of
       10,000 shares subject to options at an exercise price of $23.345 per share,
       plus $6,751,032.12 payable in respect of 281,998 shares subject to options
       at an exercise price of $23.94 per share, plus $17,878,784 payable in
       respect of 725,600 shares subject to options at an exercise price of $24.64
       per share, plus $5,864,820 payable in respect of 206,000 shares subject to
       options at an exercise price of $28.47 per share, plus $245,520 payable in
       respect of 8,000 shares subject to options at an exercise price of $30.69
       per share, plus $508,125 payable in respect of 15,000 shares subject to
       options at an exercise price of $33.875 per share, plus $614,790 payable in
       respect of 18,000 shares subject to options at an exercise price of $34.155
       per share, plus $21,637,016.19 payable in respect of 755,054 shares that
       have not yet been subject to options on the date hereof.
  
  ================================================================================
  
                                        -2-
  3
  
                                  EXPLANATORY NOTE
  
       This Registration Statement has been filed pursuant to General Instruction
  E on Form S-8, to register 5,000,000 additional securities to be offered
  pursuant to the Amended and Restated Forrester Research, Inc. 1996 Equity
  Incentive Plan (the "1996 Plan") of Forrester Research, Inc. (the "Registrant"
  or the "Company"). A registration statement on Form S-8 (No. 333-22749), filed
  with the Commission on March 4, 1997 to register 2,900,000 shares of common
  stock offered pursuant to the 1996 Plan and the 1996 Stock Option Plan for
  Non-Employee Directors is currently effective and is hereby incorporated herein
  by reference.
  
       All share numbers and per share information in this Registration Statement
  are adjusted to give effect to the two-for-one stock split paid on February 7,
  2000.
  
                                        -3-
  4
  
                                     SIGNATURES
  
       Pursuant to the requirements of the Securities Act of 1933, the Registrant
  certifies that it has reasonable grounds to believe that it meets all of the
  requirements for filing on Form S-8 and has duly caused this Registration
  Statement on Form S-8 to be signed on its behalf by the undersigned, thereunto
  duly authorized, in the City of Cambridge, The Commonwealth of Massachusetts, on
  this 8th day of February, 2000.
  
                                             FORRESTER RESEARCH, INC.
  
                                             By: /s/ Susan M. Whirty
                                                 ---------------------------------
                                                 Name:  Susan M. Whirty
                                                 Title: Chief Financial Officer,
                                                        Vice President, Operations
                                                        and General Counsel
  
                                  POWER OF ATTORNEY
                                  -----------------
  
       Pursuant to the requirement of the Securities Act of 1933, this
  Registration Statement has been signed by the following persons in the
  capacities and on the dates indicated. Each person whose signature appears below
  hereby authorizes and constitutes George F. Colony and Susan M. Whirty, with
  full power of substitution, to execute in the name of and on behalf of such
  person any amendment (including any post-effective amendment) to this
  Registration Statement, and any subsequent registration statement for the same
  offering that may be filed under Rule 462(b) under the Securities Act, and to
  file the same, with exhibits thereto, and other documents in connection
  therewith, making such changes in this Registration Statement and any subsequent
  registration statement under Rule 462(b) as the person(s) so acting deems
  appropriate.
  Signature                                Title                                            Date
  ---------                                -----                                            ----
  /s/ George F. Colony                     President, Chief Executive                       February 8, 2000
  ----------------------                   Officer and Chairman of the Board
  George F. Colony
  
  /s/ Susan M. Whirty                      Chief Financial Officer and                      February 8, 2000
  ----------------------                   General Counsel (Principal
  Susan M. Whirty                          Financial and Accounting Officer)
  
  /s/ Robert M. Galford                    Director                                         February 8, 2000
  ----------------------
  Robert M. Galford
  -4-
  5
  /s/ George R. Hornig                     Director                                         February 8, 2000
  ----------------------
  George R. Hornig
  
  /s/ Michael H. Welles                    Director                                         February 8, 2000
  ----------------------
  Michael H. Welles
  
  /s/ Henk W. Broeders                     Director                                         February 8, 2000
  ----------------------
  Henk W. Broeders
  -5-
  6
  
                                    EXHIBIT INDEX
  Number                         Title of Exhibit                                       Page
  ------                         ----------------                                       ----
  5                             Opinion of Ropes & Gray
  
  23.1                           Consent of Arthur Andersen LLP
  
  23.2                           Consent of Ropes & Gray (contained in the
                                 opinion filed as Exhibit 5 hereto)
  
  24.                            Power of Attorney (included as part of the
                                 signature page filed herewith)
  -6-