Exhibit 5.1

                          Ambac Financial Group, Inc.
                             One State Street Plaza
                               New York, NY 10004



                                April 27, 2001



Ambac Financial Group, Inc.
One State Street Plaza
New York, NY 10004


          Re:  Ambac Financial Group, Inc.
               Registration Statement on Form S-3
               ----------------------------------

Ladies and Gentlemen:

          This opinion is furnished by me as Assistant General Counsel for Ambac
Financial Group, Inc., a Delaware corporation (the "Company"), in connection
with the Registration Statement on Form S-3, which Registration Statement also
constitutes Post-Effective Amendment No. 1 to Registration Statement on Form S-3
(File No. 333-43695) (collectively, the "Registration Statement") to be filed on
the date hereof by the Company with the Securities and Exchange Commission (the
"Commission").  The Registration Statement which contains a combined prospectus
in accordance with Rule 429 of the General Rules and Regulations promulgated
under the Securities Act, as amended  (the "Securities Act"), relates to the
issuance and sale from time to time, pursuant to Rule 415 of the General Rules
and Regulations promulgated under the Securities Act of 1933, as amended (the
"Securities Act"), of the following securities of the Company with an aggregate
initial public offering price of up to $550,000,000: (i) debt securities, which
may be secured or unsecured, in one or more series (the "Debt Securities"),
which may be issued under the Indenture, dated as of March 15, 2001, between the
Company and First Union National Bank, as trustee (the "Indenture" and the
trustee thereunder the "Trustee"), filed as an exhibit to the Registration
Statement; (ii) shares of preferred stock, $0.01 par value (the "Preferred
Stock"), in one or more series; (iii) shares of common stock, $0.01 par value
per share, including Series A Junior Participating Preferred Stock Purchase
Rights attached thereto ("Common Stock"); and (iv) such indeterminate amount of
Debt Securities and number of shares of Preferred Stock or Common


Stock, as may be issued upon conversion, exchange or exercise of any Debt
Securities or Preferred Stock, including such shares of Preferred Stock or
Common Stock as may be issued pursuant to anti-dilution adjustments, in amounts,
at prices and on terms to be determined at the time of offering (the "Indeter-
minate Stock").  The Debt Securities, the Preferred Stock, the Common Stock and
the Indeterminate Stock are collectively referred to herein as the "Offered
Securities".

          This opinion is delivered in accordance with the requirements of Items
601(b)(5) of Regulation S-K under the Securities Act.

          I have examined and am familiar with originals or copies, certified or
otherwise identified to our satisfaction, of such documents, corporate records
and other instruments as I have deemed necessary or appropriate in connection
with this opinion, including (i) the form of Registration Statement relating to
the Offered Securities; (ii) the Indenture; (iii) the Amended and Restated
Certificate of Incorporation of the Company, as currently in effect; (iv) the
By-Laws of the Company, as currently in effect; and (v) certain resolutions
adopted to date by the Board of Directors of the Company (the "Board of
Directors") relating to the registration of the Offered Securities.

          In my examination, I have assumed the genuineness of all signatures,
the authenticity of all documents submitted to me as originals, the conformity
to original documents of all documents submitted to me as certified, conformed
or photostatic copies and the authenticity of the originals of such latter
documents. As to any facts material to the opinions expressed herein that were
not independently established or verified, I have relied upon oral or written
statements and representations of officers and other representatives of the
Company and others. I have assumed that the Indenture has been duly authorized,
executed and delivered by the Trustee and that any Debt Securities that may be
issued will be manually signed or countersigned, as the case may be, by duly
authorized officers of the Trustee.

          I am a member of the Bar in the State of New York and I do not express
any opinion as to the laws of any other jurisdiction other than the laws of the
United States of America and the General Corporation Law of the State of
Delaware, to the extent referred to specifically herein. The Offered Securities
may be issued from time to time on a delayed or continuous basis, and this
opinion is limited to the laws, including the rules and regulations, as in
effect on the date hereof.





          Based upon and subject to the foregoing, I am of the opinion that:

          1.  With respect to any series of Debt Securities (the "Offered Debt
Securities"), when (i) the Registration Statement, as finally amended (including
all necessary post-effective amendments), has become effective and the Indenture
has been qualified under the Trust Indenture Act of 1939, as amended; (ii) an
appropriate prospectus supplement or term sheet with respect to the Offered Debt
Securities has been prepared, delivered and filed in compliance with the
Securities Act and the applicable rules and regulations thereunder; (iii) if the
Offered Debt Securities are to be sold pursuant to a firm commitment
underwritten offering, an underwriting agreement with respect to the Offered
Debt Securities has been duly authorized, executed and delivered by the Company
and the other parties thereto; (iv) the Board of Directors, including any
appropriate committee appointed thereby, and appropriate officers of the Company
have taken all necessary corporate action to approve the issuance and terms of
the Offered Debt Securities and related matters; (v) the terms of the Offered
Debt Securities and of their issuance and sale have been duly established in
conformity with the Indenture so as not to violate any applicable law, the
Amended and Restated Certificate of Incorporation or By-laws of the Company or
result in a default under or breach of any agreement or instrument binding upon
the Company and so as to comply with any requirement or restriction imposed by
any court or governmental body having jurisdiction over the Company; and (vi)
the Offered Debt Securities have been duly executed and authenticated in
accordance with the provisions of the Indenture and duly delivered to the
purchasers thereof upon payment of the agreed-upon consideration therefor, the
Offered Debt Securities (including any Debt Securities duly issued upon
conversion, exchange or exercise of any Debt Securities or Preferred Stock),
when issued and sold in accordance with the Indenture and the applicable
underwriting agreement, if any, or any other duly authorized, executed and
delivered valid and binding purchase or agency agreement, will be valid and
binding obligations of the Company, enforceable against the Company in
accordance with their respective terms, except to the extent that (a)
enforcement thereof may be limited by (i) bankruptcy, insolvency,
reorganization, fraudulent conveyance, moratorium or other similar laws now or
hereafter in effect relating to creditors' rights generally, (ii) general
principles of equity (regardless of whether enforceability is considered in a
proceeding at law or in equity), and (iii) public policy considerations which
may limit the rights of the parties to obtain further remedies, and (b) the
waiver contained in Section 514 of the Indenture may be deemed unenforceable.

          2.  With respect to the shares of any series of Preferred Stock (the
"Offered Preferred Stock"), when (i) the Registration Statement, as finally
amended



(including all necessary post-effective amendments), has become effective; (ii)
an appropriate prospectus supplement or term sheet with respect to the shares of
the Offered Preferred Stock has been prepared, delivered and filed in compliance
with the Securities Act and the applicable rules and regulations thereunder;
(iii) if the Offered Preferred Stock is to be sold pursuant to a firm commitment
underwritten offering, an underwriting agreement with respect to the shares of
the Offered Preferred Stock has been duly authorized, executed and delivered by
the Company and the other parties thereto; (iv) the Board of Directors,
including any appropriate committee appointed thereby, and appropriate officers
of the Company have taken all necessary corporate action to approve the issuance
and terms of the shares of the Offered Preferred Stock and related matters,
including the adoption of a Certificate of Designation for the Offered Preferred
Stock in accordance with the applicable provisions of Delaware law (the
"Certificate of Designation") in the form to be filed as an exhibit to the
Registration Statement; any amendment thereto or any document incorporated by
reference therein; (v) the filing of the Certificate of Designation with the
Secretary of State of the State of Delaware has duly occurred; (vi) the terms of
the Offered Preferred Stock and of their issuance and sale have been duly
established in conformity with the Company's Amended and Restated Certificate of
Incorporation including the Certificate of Designation relating to the Offered
Preferred Stock and the By-laws of the Company so as not to violate any
applicable law, the Amended and Restated Certificate of Incorporation or By-laws
of the Company or result in a default under or breach of any agreement or
instrument binding upon the Company and so as to comply with any requirement or
restriction imposed by any court or governmental body having jurisdiction over
the Company; and (vii) certificates representing the shares of the Offered
Preferred Stock are duly executed, countersigned, registered and delivered upon
payment of the agreed-upon consideration therefor, the shares of the Offered
Preferred Stock (including any Preferred Stock duly issued upon conversion,
exchange or exercise of any Debt Securities or Preferred Stock), when issued or
sold in accordance with the applicable underwriting agreement or any other duly
authorized, executed and delivered valid and binding purchase or agency
agreement, will be duly authorized, validly issued, fully paid and
nonassessable.

          3.  With respect to any offering of Common Stock (the "Offered Common
Stock"), when (i) the Registration Statement, as finally amended (including all
necessary post-effective amendments), has become effective; (ii) an appropriate
prospectus supplement or term sheet with respect to the Offered Common Stock has
been prepared, delivered and filed in compliance with the Securities Act and the
applicable rules and regulations thereunder; (iii) if the Offered Common Stock
is to be sold pursuant to a firm commitment underwritten offering, an
underwriting agreement


with respect to the Offered Common Stock has been duly authorized, executed and
delivered by the Company and the other parties thereto; (iv) the Board of
Directors, including any appropriate committee appointed thereby, and
appropriate officers of the Company have taken all necessary corporate action to
approve the issuance of the Offered Common Stock and related matters; (v) the
terms of the issuance and sale of the Offered Common Stock have been duly
established in conformity with the Amended and Restated Certificate of
Incorporation and By-laws of the Company so as not to violate any applicable
law, the Amended and Restated Certificate of Incorporation or By-laws of the
Company or result in a default under or breach of any agreement or instrument
binding upon the Company and so as to comply with any requirement or restriction
imposed by any court or governmental body having jurisdiction over the Company;
and (vi) certificates representing the shares of Offered Common Stock are duly
executed, countersigned, registered and delivered upon payment of the agreed
upon consideration therefor, the shares of Offered Common Stock (including any
Common Stock duly issued upon conversion, exchange or exercise of any Debt
Securities or Preferred Stock), when issued and sold in accordance with the
applicable underwriting agreement with respect to the Offered Common Stock or
any other duly authorized, executed and delivered valid and binding purchase or
agency agreement, will be duly authorized, validly issued, fully paid and
nonassessable, provided that the consideration therefor is not less than the par
value thereof.

          I hereby consent to the filing of this opinion with the Commission as
Exhibit 5.1 to the Registration Statement.  I also consent to the reference to
me under the heading "Legal Opinions" in the Registration Statement.  In giving
this consent, I do not thereby admit that I am in the category of persons whose
consent is required under Section 7 of the Securities Act or the Rules and
Regulations of the Commission promulgated thereunder.  This opinion is
expressed as of the date hereof unless otherwise expressly stated, and I
disclaim any undertaking to advise you of any subsequent changes of the facts
stated or assumed herein or any subsequent changes in applicable law.

                               Very truly yours,

                               /s/ ANNE G. GILL, ESQ.