EXHIBIT 5.1
                                          
                                          
                                          
                                          
                                    May 7, 1999
                                          
                                          
AdForce, Inc.
10590 North Tantau Avenue
Cupertino, California 95014

Gentlemen/Ladies:

     At your request, we have examined the Registration Statement on Form S-8
(the "REGISTRATION STATEMENT") to be filed by you with the Securities and
Exchange Commission (the "COMMISSION") on or about May 7, 1999 in connection
with the registration under the Securities Act of 1933, as amended, of an
aggregate of 5,470,110 shares of your Common Stock (the "STOCK") subject to
issuance by you upon the exercise of: (1) options to purchase up to 2,003,989
shares of Stock granted under the Company's 1997 Stock Plan (the "1997 PLAN");
(2) options to purchase 6,598 shares of Stock granted by you under the StarPoint
Software, Inc. 1996 Stock Plan (the "STARPOINT PLAN"); (3) options to purchase
up to 2,249,523 shares of Stock granted or to be granted under the Company's
1999 Equity Incentive Plan (the "1999 OPTION PLAN"); (4) options to purchase up
to 200,000 shares of Stock granted or to be granted under the Company's 1999
Directors Stock Option Plan (the "1999 DIRECTORS PLAN"); (5) purchase rights for
up to 300,000 shares of Stock granted or to be granted under the Company's 1999
Employee Stock Purchase Plan (the "1999 PURCHASE PLAN"); and (6) options to
purchase up to 710,000 shares of Stock granted pursuant to non-plan option
agreements (the "NON-PLAN AGREEMENTS").  The plans referred to in clauses 
(1) through (6) above are collectively referred to in this letter as the 
"PLANS." In rendering this opinion, we have examined the following:

     (1)  your registration statement on Form S-1 (File No. 333-73231) filed
          with, and declared effective by, the Commission on May 7, 1999, 
          together with the Exhibits filed as a part thereof, including without
          limitation, each of the Plans and related stock option grant or 
          purchase and exercise agreements;

     (2)  your registration statement on Form 8-A (File No. 000-25497), filed
          with the Commission on May 4, 1999, together with the order of
          effectiveness issued by the Commission therefor on May 7, 1999;

     (3)  the Registration Statement, together with the Exhibits filed as a part
          thereof;

     (4)  the Prospectuses prepared in connection with the Registration
          Statement;

     (5)  the minutes of meetings and actions by written consent of the
          stockholders and Board of Directors that are contained in your minute
          books and the minute books of your predecessor, Imgis, Inc., a
          California corporation ("IMGIS CALIFORNIA"), that are in our
          possession;



AdForce, Inc.
May 7, 1999
Page 2

     (6)  the stock records that you have provided to us (consisting of a list
          of stockholders of even date herewith and a list of option and warrant
          holders of even date herewith respecting your capital and of any
          rights to purchase capital stock, which you have represented to us 
          are true and complete as of their dates); and

     (7)  a Management Certificate addressed to us and dated of even date
          herewith executed by the Company containing certain factual and other
          representations.
     
     
     We have also confirmed the continued effectiveness of your registration 
under the Securities Exchange Act of 1934, as amended, by telephone call to 
the offices of the Commission and have confirmed your eligibility to use Form 
S-8.
     
     In our examination of documents for purposes of this opinion, we have 
assumed, and express no opinion as to, the genuineness of all signatures on 
original documents, the authenticity of all documents submitted to us as 
originals, the conformity to originals of all documents submitted to us as 
copies, the legal capacity of all natural persons executing the same, the 
lack of any undisclosed terminations, modifications, waivers or amendments to 
any documents reviewed by us and the due authorization, execution and 
delivery of all documents where due authorization, execution and delivery are 
prerequisites to the effectiveness thereof.
     
     As to matters of fact relevant to this opinion, we have relied solely upon
our examination of the documents referred to above and have assumed the current
accuracy and completeness of the information obtained from public officials and
records referred to above.  We have made no independent investigation or other
attempt to verify the accuracy of any of such information or to determine the
existence or non-existence of any other factual matters; HOWEVER, we are not
aware of any facts that would cause us to believe that the opinion expressed
herein is not accurate.
     
     We are admitted to practice law in the State of California, and we express
no opinion herein with respect to the application or effect of the laws of any
jurisdiction other than the existing laws of the United States of America and
the State of California and (without reference to case law or secondary sources)
the existing Delaware General Corporation Law.
     
     In connection with our opinion expressed below, we have assumed that, at or
prior to the time of the delivery of any shares of Stock, the Registration
Statement will have become effective under the Securities Act of 1933, as
amended, that the registration will apply to such shares of Stock and will not
have been modified or rescinded and that there will not have occurred any change
in law affecting the validity or enforceability of such shares of Stock.
     
     Based upon the foregoing, it is our opinion that the 5,470,110 shares of
Stock that may be issued and sold by you upon the exercise of: (1) stock options
granted under the 1997 Plan; (2) stock options granted under the StarPoint Plan;
(3) stock options granted or to be granted under the 1999 Option Plan; (4) stock
options granted or to be granted under the 1999 Directors 



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May 7, 1999
Page 3

Plan; (5) purchase rights granted or to be granted under the 1999 Purchase 
Plan; and (6) stock options granted under Non-Plan Agreements, when issued 
and sold in accordance with the applicable plan and stock option grant and 
exercise agreements or stock purchase agreements entered into or to be 
entered into thereunder, and in the manner referred to in the relevant 
Prospectus associated with the Registration Statement, will be validly 
issued, fully paid and nonassessable.
     
     We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to all references to us, if any, in the
Registration Statement, the Prospectus constituting a part thereof and any
amendments thereto.
     
     This opinion speaks only as of its date and we assume no obligation to
update this opinion should circumstances change after the date hereof.  This
opinion is intended solely for the your use as an exhibit to the Registration
Statement for the purpose of the above sale of the Stock and is not to be relied
upon for any other purpose.
                                   
                                   Very truly yours,
                                   
                                   /s/ FENWICK & WEST LLP