Guggenheim Funds Distributors, Inc.

                            2455 Corporate West Drive
                              Lisle, Illinois 60532


                                  March 7, 2011


Securities and Exchange Commission
100 F Street, N.E.
Washington, DC 20549


Re: Guggenheim Defined Portfolios, Series 766
    File No. 333-171992


Ladies/Gentlemen:

   The undersigned, Guggenheim Defined Portfolios, Series 766 (the "Trust"), by
Guggenheim Funds Distributors, Inc., as the sponsor and depositor of the Trust
and of the units covered by the subject Registration Statement, pursuant to the
provisions of Rule 461 of the General Rules and Regulations of the Securities
and Exchange Commission under the Securities Act of 1933, hereby respectfully
requests that the Securities and Exchange Commission consent to the filing of
the amendment to the Registration Statement and grant acceleration of the
effectiveness of said Registration Statement, as amended, so that the same may
become effective as early as practicable on March 9, 2011 or as soon thereafter
as possible.

Very truly yours,

Guggenheim Defined Portfolios, Series 766

By: Guggenheim Funds Distributors, Inc.


By: /S/ Kevin Robinson
Kevin Robinson

Senior Managing Director, General Counsel and Secretary