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                                                                       Exhibit 5

                       SHAW, PITTMAN, POTTS & TROWBRIDGE
                              2300 N Street, N.W.
                            Washington, D.C.   20037





August 11, 1998


Landmark Systems Corporation
8000 Towers Crescent Drive
Vienna, Virginia  22180

Re:      Landmark Systems Corporation
         Registration Statement on Form S-8

 Ladies and Gentlemen:

         We have acted as counsel to Landmark Systems Corporation, a Virginia
corporation (the "Company"), in connection with the registration of 1,000,000
shares (the "Shares") of the Common Stock, $0.01 par value, of the Company
pursuant to a Registration Statement on Form S-8 under the Securities Act of
1933 (the "Registration Statement"), relating to the Landmark Systems
Corporation 1998 Employee Stock Purchase Plan (the "Plan").

         Based upon our examination of the originals or copies of such
documents, corporate records, certificates of officers of the Company and other
instruments as we have deemed necessary and upon the laws as presently in
effect, we are of the opinion that the Shares have been duly authorized for
issuance by the Company, and that upon issuance and delivery in accordance with
the Plans referred to in the Registration Statement, the Shares will be validly
issued, fully paid and nonassessable.

         We hereby consent to the filing of this opinion as Exhibit 5 to the
Registration Statement.

                                        Very truly yours,

                                        /s/ SHAW, PITTMAN, POTTS & TROWBRIDGE

                                        SHAW, PITTMAN, POTTS & TROWBRIDGE