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                                   EXHIBIT 5.1

                            HAYNES AND BOONE, L.L.P.
                        1000 Louisiana Street, Suite 4300
                              Houston, Texas 77002
                                 (713) 547-2000

May 15, 2001

Input/Output, Inc.
12300 C. E. Selecman Drive
Stafford, Texas  77477

Gentlemen:

We have acted as counsel to Input/Output, Inc., a Delaware corporation (the
"Company"), in connection with the preparation of the Registration Statement on
Form S-8 (the "Registration Statement") filed with the Securities and Exchange
Commission under the Securities Act of 1933, as amended, relating to the
registration of 100,000 shares of Common Stock, par value $0.01 per share (the
"Common Stock"), of the Company that may be issued pursuant to the terms of the
Company's Non-Employee Directors' Retainer Plan (the "Plan").

In connection therewith, we have examined (i) the Certificate of Incorporation
and the Bylaws of the Company, each as amended; (ii) minutes and records of the
corporate proceedings of the Company with respect to the adoption of the Plan;
(iii) certificates of certain officers and directors of the Company; (iv) the
Plan; and (v) such other documents as we have deemed necessary for the
expression of the opinions contained herein.

In making the foregoing examination, we have assumed the genuineness of all
signatures and the authenticity of all documents submitted to us as originals,
and the conformity to original documents of all documents submitted to us as
certified or photostatic copies. Furthermore, we have assumed that prices paid
for shares of Common Stock will equal or exceed the par value per share of the
Common Stock. As to questions of fact material to this opinion, where such facts
have not been independently established, and as to the content and form of the
Certificate of Incorporation (as amended), Bylaws (as amended), minutes,
records, resolutions and other documents or writings of the Company, we have
relied, to the extent we deem reasonably appropriate, upon representations or
certificates of officers or directors of the Company and upon documents, records
and instruments furnished to us by the Company, without independent check or
verification of their accuracy.

Based upon the foregoing, and having due regard for such legal considerations as
we deem relevant, we are of the opinion that the 100,000 shares of Common Stock
of the Company covered by the Registration Statement, which may be issued from
time to time in accordance with the terms of the Plan, have been duly authorized
for issuance by the Company, and, when so issued in accordance with the terms
and conditions of the Plan, will be validly issued, fully paid and
nonassessable.

We hereby consent to the filing of this opinion with the Securities and Exchange
Commission as an exhibit to the Registration Statement.


                                          Very truly yours,

                                          /s/ Haynes and Boone, L.L.P.