EXHIBIT 3.1


                             CHAPMAN AND CUTLER LLP
                             111 West Monroe Street
                             Chicago, Illinois 60603


                                   May 1, 2008


Van Kampen Funds Inc.
522 Fifth Avenue
New York, New York 10036


                Re: Van Kampen Unit Trusts, Municipal Series 689
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Ladies/Gentlemen:

     We have served as counsel for Van Kampen Unit Trusts, Municipal Series 689
(the "Fund"), in connection with the preparation, execution and delivery of a
trust agreement dated May 1, 2008 (the "Trust Agreement") between Van Kampen
Funds Inc., as depositor (the "Depositor"), Standard & Poor's Securities
Evaluations, Inc., as evaluator, Van Kampen Asset Management, as supervisor, and
The Bank of New York, as trustee (the "Trustee"), pursuant to which the
Depositor has delivered to and deposited bonds listed in the schedules to the
Trust Agreement with the Trustee and pursuant to which the Trustee has issued to
or on the order of the Depositor a certificate or certificates representing
units of fractional undivided interest in and ownership of the trust (the
"Trust") of said Fund (the "Units") created under said Trust Agreement.

     In connection therewith, we have examined such pertinent records and
documents and matters of law as we have deemed necessary in order to enable us
to express the opinions hereinafter set forth.

     Based upon the foregoing, we are of the opinion that:

     1.   The execution and delivery of the Trust Agreement and the execution
          and issuance of certificates evidencing the Units in the Trust of the
          Fund have been duly authorized; and

     2.   The certificates evidencing the Units in the Trust of the Fund when
          duly executed and delivered by the Depositor and the Trustee in
          accordance with the aforementioned Trust Agreement, will constitute
          valid and binding obligations of such Trusts and the Depositor in
          accordance with the terms thereof and such Units, when issued and
          delivered in accordance with the Trust Agreement against payment of
          the consideration set forth in the Trust prospectus, will be validly
          issued, fully paid and non-assessable.

     We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement (File No. 333-149154) relating to the Units referred to
above and to the use of our name and to the reference to our firm in said
Registration Statement and in the related Prospectus.

                                                         Respectfully submitted,


                                                          CHAPMAN AND CUTLER LLP