

                                                                     EXHIBIT 5.1


                                 August 10, 1999


TRIMBLE NAVIGATION LIMITED
645 North Mary Avenue
Sunnyvale, California 94088

         RE:      REGISTRATION STATEMENT ON FORM S-8

Ladies and Gentlemen:

     We have examined the Registration  Statement on Form S-8 to be filed by you
with the  Securities  and Exchange  Commission  on or about August 11, 1999 (the
"Registration  Statement"),  in  connection  with  the  registration  under  the
Securities  Act of 1933,  as amended,  of 600,000  shares of your  Common  Stock
reserved  for  issuance  under  the 1988  Employee  Stock  Purchase  Plan and of
1,200,000 shares of your Common Stock reserved for issuance under the 1993 Stock
Option  Plan  (the  "Plans").  As  your  legal  counsel,  we have  examined  the
proceedings  taken and  proposed to be taken in  connection  with the  issuance,
sale, and payment of consideration for the shares to be issued under the Plans.

     It is our opinion that,  when issued and sold in the manner  referred to in
the Plans and pursuant to the agreements  which accompany the Plans,  the shares
will be legally and validly issued, fully paid, and non-assessable.

     We  consent to the use of this  opinion  as an exhibit to the  Registration
Statement and further  consent to the use of our name wherever  appearing in the
Registration Statement and any amendments thereto.

                                         Very truly yours,

                                         WILSON, SONSINI, GOODRICH & ROSATI
                                         Professional Corporation


                                         By:/s/John B. Goodrich
                                               -----------------
                                               John B. Goodrich


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