EXHIBIT 5.1 [Letterhead of Citigroup Inc.] Citigroup Inc. 425 Park Avenue New York, NY 10043 December 22, 2004 Citibank Credit Card Issuance Trust c/o Citibank (South Dakota), National Association, as Managing Beneficiary 701 East 60th Street, North Mail Code 1251 Sioux Falls, South Dakota 57117 Citibank Credit Card Master Trust I c/o Citibank (South Dakota), National Association, as Servicer 701 East 60th Street, North Sioux Falls, South Dakota 57117 Citibank (South Dakota), National Association 701 East 60th Street, North Sioux Falls, South Dakota 57117 Citibank (Nevada), National Association 8725 West Sahara Avenue Las Vegas, Nevada 89163 Re: Registration Statement on Form S-3 Ladies and Gentlemen: I am the General Counsel for Capital Markets of Citigroup Inc. I have acted as counsel to Citibank (South Dakota), National Association ("Citibank (South Dakota)"), Citibank (Nevada), National Association ("Citibank (Nevada)" and, together with Citibank (South Dakota), the "Banks"), Citibank Credit Card Issuance Trust (the "Issuance Trust") and Citibank Credit Card Master Trust I (the "Master Trust") in connection with the filing on the date hereof by such persons with the Securities and Exchange Commission (the "Commission") of Amendment No. 1 to Registration Statement on Form S-3 (the "Registration Statement") registering under the Securities Act of 1933, as amended (the "Act"), both a collateral certificate representing an undivided interest in certain assets of the Master Trust (the "Collateral Certificate") and series of notes secured by the Collateral Certificate (the "Notes"). The Collateral Certificate has been issued pursuant to the Amended and Restated Pooling and Servicing Agreement dated as of October 5, 2001, as amended by Amendment No. 1 thereto dated as of December 31, 2003 (as so amended, the "Pooling and Servicing Agreement"), among Citibank (South Dakota), as Seller and Servicer, Citibank (Nevada), as Seller, and Deutsche Bank Trust Company Americas (formerly Bankers Trust Company), as Trustee (the "Master Citibank Credit Card Issuance Trust Citibank Credit Card Master Trust I Citibank (South Dakota), National Association Citibank (Nevada), National Association Page 2 Trust Trustee"), which are incorporated by reference as Exhibit 4.4 and Exhibit 4.5, respectively, to the Registration Statement, and a related Series Supplement dated as of September 26, 2000 to the Pooling and Servicing Agreement (the "Series Supplement") among Citibank (South Dakota), as Seller and Servicer, Citibank (Nevada), as Seller, and the Master Trust Trustee, which is incorporated by reference as Exhibit 4.3 to the Registration Statement. The Notes will be issued under an Indenture dated as of September 26, 2000 between the Issuance Trust and Deutsche Bank Trust Company Americas (formerly Bankers Trust Company), as Trustee (the "Indenture Trustee"), which is incorporated by reference as Exhibit 4.1 to the Registration Statement, as amended by Amendment No. 1 thereto, which is incorporated by reference as Exhibit 4.2 to the Registration Statement (as so amended, the "Indenture"). I, or attorneys under my supervision, have examined and am familiar with originals, or copies certified or otherwise identified to my satisfaction, of such corporate records, certificates or documents as I have deemed appropriate as a basis for the opinions expressed below. In such examination, I (or such persons) have assumed the legal capacity of all natural persons, the genuineness of all signatures, the authenticity of all documents submitted to me (or such persons) as originals, the conformity to original documents of all documents submitted to me (or such persons) as certified or photostatic copies and the authenticity of the originals of such copies. Based upon and subject to the foregoing and assuming that (i) the Registration Statement and any amendments thereto (including post-effective amendments) will have become effective and comply with all applicable laws at the time the Notes are offered or issued as contemplated by the Registration Statement; (ii) a Prospectus Supplement will have been prepared and filed with the Commission describing the Notes offered thereby and will comply with all applicable laws; (iii) all Notes will be issued and sold in compliance with applicable federal and state laws and in the manner stated in the Registration Statement and the appropriate Prospectus Supplement; (iv) a definitive underwriting, selling agent, purchase or similar agreement and any other necessary agreement with respect to Notes offered or issued will have been duly authorized and validly executed and delivered by the parties thereto; (v) the Notes will be sold and delivered at the price and in accordance with the terms of such agreement and as set forth in the Registration Statement and the Prospectus Supplement(s) referred to therein, (vi) the Issuance Trust will authorize the issuance of the Notes and the terms and conditions thereof and will take all other appropriate additional action, (vii) each of the Banks has taken all other appropriate action in connection with the authorization and issuance of the Collateral Certificate, (viii) at the time of execution, authentication, issuance and delivery of the Collateral Certificate, the related Series Supplement was duly authorized, executed and delivered by the Master Trust Trustee, (ix) at the time of execution, authentication, issuance and delivery of the Notes, the Indenture will have been duly authorized, executed and delivered by the Issuance Trust and the Indenture Trustee, and (x) the Indenture and the Indenture Trustee have been duly qualified under the Trust Indenture Act of 1939, I am of the opinion that: Citibank Credit Card Issuance Trust Citibank Credit Card Master Trust I Citibank (South Dakota), National Association Citibank (Nevada), National Association Page 3 1. The Pooling and Servicing Agreement has been duly authorized, executed and delivered by each of the Banks, and assuming due authorization, execution and delivery by the Master Trust Trustee, the Pooling and Servicing Agreement constitutes binding obligations of the Banks. 2. The Series Supplement relating to the Collateral Certificate has been duly authorized, executed and delivered by each of the Banks, and assuming due authorization, execution and delivery by the Master Trust Trustee, such Series Supplement constitutes binding obligations of the Banks. 3. The Collateral Certificate has been duly authorized, executed and delivered by each of the Banks in accordance with the Pooling and Servicing Agreement and the applicable Series Supplement, and the Collateral Certificate is validly issued, fully paid and non-assessable, and entitled to the benefits provided by the Pooling and Servicing Agreement and the applicable Series Supplement. 4. When the Notes have been duly executed, authenticated, issued and delivered in accordance with the provisions of the Indenture, the Notes will be validly issued, fully paid, non-assessable and binding obligations of the Issuance Trust, and the holders of the Notes will be entitled to the benefits of the Indenture. Insofar as my opinion relates to the validity, binding effect or enforceability of any agreement or obligation, it is subject to applicable bankruptcy, insolvency, reorganization, fraudulent conveyance, moratorium or other similar laws affecting creditors' rights generally from time to time in effect and subject to general principles of equity, regardless of whether such is considered in a proceeding in equity or at law. My opinion is limited to matters governed by the Federal laws of the United States of America, the laws of the State of New York and the General Corporation Law of the State of Delaware (including the applicable provisions of the Delaware Constitution and the reported judicial decisions interpreting the General Corporation Law of the State of Delaware and such applicable provisions of the Delaware Constitution). I am not admitted to the practice of law in the State of Delaware. Citibank Credit Card Issuance Trust Citibank Credit Card Master Trust I Citibank (South Dakota), National Association Citibank (Nevada), National Association Page 4 I consent to the use of this opinion in the Registration Statement and to the reference to my name in the Prospectus constituting a part of such Registration Statement under the heading "Legal Matters". In giving such consent, I do not thereby admit that I come within the category of persons whose consent is required under Section 7 of the Act, or the rules and regulations of the Commission thereunder. Very truly yours, /s/ John R. Dye John R. Dye