EXHIBIT 5.1

                              Greater Bay Bancorp
                        400 Emerson Street, 3/rd/ Floor
                          Palo Alto, California 94301


June 27, 2000


Greater Bay Bancorp
2860 West Bayshore Road
Palo Alto, CA 94303

     Re:  Registration Statement on Form S-4

Ladies and Gentlemen:

     As General Counsel of Greater Bay Bancorp (the "Company"), at your request,
I have examined the Registration Statement on Form S-4 (the "Registration
Statement") being filed by the Company with the Securities and Exchange
Commission (the "SEC") in connection with the registration under the Securities
Act of 1933, as amended (the "Securities Act"), of up to 1,133,045 shares of
common stock, no par value, of the Company (the "Shares") issuable in connection
with the Agreement and Plan of Reorganization, dated as of March 21, 2000, by
and among the Company, Bank of Petaluma and DKSS Corp. (the "Agreement").

     I have examined such instruments, documents and records which I deemed
relevant and necessary for the basis of my opinion hereinafter expressed. In
such examination, I have assumed the genuineness of all signatures and the
authenticity of all documents submitted to me as originals and the conformity to
the originals of all documents submitted to me as copies.

     Based upon the foregoing and the other assumptions contained herein, it is
the opinion of the undersigned that the Shares issuable by the Company pursuant
to the Agreement will be, when issued and delivered in accordance with the
Agreement and the Registration Statement, duly authorized, validly issued, fully
paid and non-assessable.

     This opinion is further subject to the following assumptions: (i) the
consideration for the Shares to be issued pursuant to the Agreement will be
received prior to the issuance thereof, (ii) the Shares to be issued pursuant to
the Agreement will be issued in accordance with the terms of the Agreement,
(iii) the Registration Statement will become effective under the Securities Act
prior to the issuance of the Shares under the Agreement and no stop order
suspending the effectiveness of the Registration Statement shall have been
issued and no proceedings for that purpose shall have been instituted or be
pending before the SEC, and (iv) the issuance of the Shares pursuant to the
Agreement will comply with the securities laws of each state or jurisdiction
applicable thereto (other than the Securities Act).

     This opinion is issued to you solely for use in connection with the
Registration Statement and is not to be quoted or otherwise referred to in any
financial statements of the Company or


Greater Bay Bancrop
Page 2

related document, nor is it to be filed with or furnished to any government
agency or other person, without my prior written consent.

     I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement which is being filed by the Company in connection with
the registration of the Shares under the Securities Act.


Very truly yours,

/s/ Linda M. Iannone

Linda M. Iannone
Senior Vice President, General Counsel and Secretary

                                       2