Exhibit 5.1 [Debevoise & Plimpton Letterhead LLP] March 12, 2004 The Hartford Financial Services Group, Inc. Hartford Plaza Hartford, Connecticut 06115 Ladies and Gentlemen: This opinion is furnished to you in connection with the Registration Statement on Form S-3 (File No. 333-108067) (the "Registration Statement") and the Prospectus Supplement, dated March 4, 2004 (the "Prospectus Supplement"), to the Prospectus dated December 3, 2003, of The Hartford Financial Services Group, Inc., a Delaware corporation (the "Company"), filed with the Securities and Exchange Commission (the "Commission"), relating to the issuance and sale by the Company of $200,000,000 aggregate principal amount of the Company's 4.75% Senior Notes due March 1, 2014 (the "Notes") issued pursuant to the Senior Indenture (the "Indenture"), dated as of March 9, 2004 between the Company and JPMorgan Chase Bank, as trustee. In so acting, we have examined and relied upon the originals or certified, conformed or reproduction copies of such agreements, instruments, documents, records and certificates of the Company, such certificates of public officials and such other documents, and have made such investigations of law, as we have deemed necessary or appropriate for the purposes of the opinions expressed below. In all such examinations, we have assumed without independent investigation or inquiry the legal capacity of all natural persons executing documents, the genuineness of all signatures on original or certified copies, the authenticity of all original or certified copies and the conformity to original or certified documents of all copies submitted to us as conformed or reproduction copies. We have relied as to factual matters upon, and have assumed the accuracy of, the statements made in the certificates of officers of the Company delivered to us and certificates and other statements or information of or from public officials and officers and representatives of the Company. Based on and subject to the foregoing, we are of the opinion that the Notes have been validly issued and constitute valid and binding obligations of the Company entitled to the benefits provided by the Indenture. The opinion set forth above is subject to the effects of (1) bankruptcy, insolvency, reorganization, fraudulent conveyance, moratorium and other similar laws now or hereafter in effect affecting creditors' rights generally, (2) general principles of equity (regardless of whether enforceability is considered in a proceeding in law or equity), (3) an implied covenant of good faith, reasonableness and fair dealing, and standards of materiality and (4) limitations with respect to enforceability of provisions of the Indenture providing for indemnification or contribution, arising under applicable law (including court decisions) or public policy. The opinion expressed herein is limited to the laws of the State of New York as currently in effect and we do not express any opinion herein concerning any other laws. We hereby consent to the filing of this opinion as an exhibit to the Company's Form 8-K filed on March 12, 2004, incorporated by reference in the Registration Statement, and to the reference to our firm under the caption "Validity of the Notes" in the Prospectus Supplement. In giving such consent, we do not thereby concede that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission thereunder. Very truly yours, /s/ Debevoise & Plimpton LLP 2