Exhibit No. 5.1 AMBAC FINANCIAL GROUP, INC. (a Delaware corporation) Senior Debt Securities TERMS AGREEMENT April 1, 1998 To: Ambac Financial Group, Inc. One State Street Plaza New York, New York 10004 Ladies and Gentlemen: We understand that Ambac Financial Group, Inc., a Delaware corporation (the "Company"), proposes to issue and sell $200,000,000 aggregate principal amount of its Senior Debt Securities (such securities being hereinafter referred to as the "Underwritten Securities"). Subject to the terms and conditions set forth and incorporated by reference herein, the underwriters named below (the "Underwriters") offer to purchase, severally and not jointly, the principal amount of Underwritten Securities set forth opposite their names below at the purchase price set forth below. Principal Amount of Underwriter Underwritten Securities Merrill Lynch, Pierce, Fenner & Smith Incorporated................................. $33,600,000 Goldman, Sachs & Co............................. 33,600,000 PaineWebber Incorporated........................ 33,600,000 Prudential Securities Incorporated.............. 33,600,000 Smith Barney Inc................................ 33,600,000 BT Alex. Brown Incorporated..................... 2,000,000 Robert W. Baird & Co. Incorporated.............. 2,000,000 Bear, Stearns & Co. Inc......................... 2,000,000 CIBC Oppenheimer Corp........................... 2,000,000 Cowen & Company................................. 2,000,000 Dain Rauscher Incorporated...................... 2,000,000 Donaldson, Lufkin & Jenrette Securities Corporation........................ 2,000,000 A.G. Edwards & Sons, Inc........................ 2,000,000 EVEREN Securities, Inc.......................... 2,000,000 Legg Mason Wood Walker, Incorporated............ 2,000,000 Piper Jaffray Inc............................... 2,000,000 Raymond James & Associates, Inc................. 2,000,000 The Robinson-Humphrey Company, LLC.............. 2,000,000 Tucker Anthony Incorporated..................... 2,000,000 US Clearing Corp................................ 2,000,000 Wheat First Securities, Inc..................... 2,000,000 ------------ Total........................................... $200,000,000 ============ The Underwritten Securities shall have the following terms: Title: 7.08% Debentures Due March 31, 2098. Rank: Senior Debt. Ratings: Moody's Investor's Service, Inc. - Aa2 and Standard & Poor's Ratings Group - AA. Aggregate principal amount: $200,000,000. Denominations: $25.00 and integral multiples thereof. Currency of payment: United States Dollars. Interest rate or formula: 7.08% per annum. Interest payment dates: Each March 31, June 30, September 30 and December 31. Regular record dates: Each March 15, June 15, September 15 and December 15. Stated maturity date: March 31, 2098. Redemption provisions: Except as set forth below, the Debentures are not redeemable prior to March 31, 2003. On or after March 31, 2003, the Company, at its option, may redeem the Debentures, in whole at any time or in part from time to time, on not less than 30 days but not more than 60 days notice, at a redemption price equal to 100% of the principal amount, plus accrued interest to the date of redemption. In addition, under certain circumstances involving a Tax Event, the Company will have the right, within 90 days following the occurrence of such Tax Event, to redeem the Debentures in whole (but not in part) at 100% of their principal amount, plus accrued interest to the date of redemption, as more fully described in the Prospectus Supplement. Right to Shorten Maturity: Upon the occurrence of a Tax Event (as defined in the Prospectus Supplement), the Company will have the right to shorten the maturity of the Debentures to the minimum extent required such that, after shortening the maturity, the Company will be able to deduct interest paid on the Debentures for United States federal income tax purposes, as more fully described in the Prospectus Supplement. Sinking fund requirements: None. Conversion provisions: None. Listing requirements: The Company will make application to list the Debentures for trading on the New York Stock Exchange. Black-out provisions: Between the date hereof and April 15, 1998, the Company will not, without the prior written consent of the Representatives, directly or indirectly, issue, sell, offer or contract to sell, grant any option for the sale of, or otherwise dispose of, any debt securities of the Company. Fixed or Variable Price Offering: Fixed Price Offering Initial public offering price: 100% of the principal amount, plus accrued interest, if any, from April 6, 1998. Purchase price: 96.85% of the principal amount. Form: Global certificates representing the Underwritten Securities registered in the name of Cede & Co., as nominee for The Depository Trust Company. Other terms and conditions: The Underwritten Securities will be issued under an indenture, dated as of April 1, 1998 between the Company and First Union National Bank, as Trustee (the "1998 Indenture"). All references to the "Indenture" in the Underwriting Agreement shall be deemed to refer to the 1998 Indenture. Closing date and location: April 6, 1998; Brown & Wood LLP, One World Trade Center, New York, New York 10048. Co-Managers/Representatives: Merrill Lynch, Pierce, Fenner & Smith Incorporated, Goldman, Sachs & Co., PaineWebber Incorporated, Prudential Securities Incorporated and Smith Barney Inc. Notices: Notices to the Underwriters shall be directed to the Representatives, c/o Merrill Lynch, Pierce, Fenner & Smith Incorporated, World Financial Center, North Tower, New York, New York 10281-1201, Attention: Tony Ursano. All of the provisions contained in the Company's Underwriting Agreement, dated April 1, 1998 (the "Underwriting Agreement"), are hereby incorporated by reference in their entirety herein and shall be deemed to be a part of this Terms Agreement to the same extent as if such provisions had been set forth in full herein. Unless otherwise specified herein, terms defined in the Underwriting Agreement are used herein as therein defined. This Agreement shall be governed by the laws of the State of New York applicable to agreements made and to be performed wholly within such State. If the foregoing is in accordance with your understanding of the agreement among the Underwriters and the Company, please sign and return to the undersigned a counterpart hereof, whereupon this instrument, along with all counterparts and together with the Underwriting Agreement, shall be a binding agreement among the Underwriters named herein and the Company in accordance with its terms and the terms of the Underwriting Agreement. Very truly yours, MERRILL LYNCH, PIERCE, FENNER & SMITH INCORPORATED GOLDMAN, SACHS & CO. PAINEWEBBER INCORPORATED PRUDENTIAL SECURITIES INCORPORATED SMITH BARNEY INC. By: Merrill Lynch, Pierce, Fenner & Smith Incorporated By _______________________________________ Authorized Signatory Acting on behalf of itself and as Representative of the other named Underwriters. Accepted: AMBAC FINANCIAL GROUP, INC. By _________________________________ Name: Richard B. Gross Title: Senior Vice President, General Counsel and Secretary