Exhibit 5.1

                [Letterhead of Wilson Sonsini Goodrich & Rosati]

                                November 12, 2002


         Nanometrics Incorporated
         1550 Buckeye Drive
         Milpitas, CA 95035

                Re:  Nanometrics Incorporated 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 ("SEC") on or about November 12,
2002 (the "Registration  Statement"),  in connection with the registration under
the Securities Act of 1933, as amended, of 1,200,000 shares of your Common Stock
(the "Shares")  reserved for issuance under the  Nanometrics  Incorporated  2002
Nonstatutory  Stock Option Plan (the  "Plan").  As your legal  counsel,  we have
examined and are familiar with the  proceedings  taken by you in connection with
the sale of the Shares pursuant to the Plan.

         It is our opinion  that the Shares,  when issued and sold in the manner
described in the Plan and pursuant to the agreement that  accompanies each grant
under the Plan, 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 the use of our name wherever  appearing in the
Registration  Statement,  including the Prospectus  constituting a part thereof,
and any amendments thereto.

                                        Very truly yours,

                                        /s/ Wilson Sonsini Goodrich & Rosati

                                        WILSON SONSINI GOODRICH & ROSATI
                                        Professional Corporation

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