Exhibit 5(b)

                              DEWEY BALLANTINE LLP

                           1301 AVENUE OF THE AMERICAS
                          NEW YORK, NEW YORK 10019-6092
                        TEL 212 259-8000 FAX 212 259-6333

                                                  December 11, 2006

Avista Corporation
1411 East Mission Avenue
Spokane, WA 99202

Ladies and Gentlemen:

      We are acting as counsel to Avista Corporation, a Washington corporation
(the "Company"), in connection with the filing by the Company of a Registration
Statement on Form S-3 (the "Registration Statement") under the Securities Act of
1933, as amended (the "Act"), relating to the registration of (1) secured debt
securities (the "Secured Debt Securities") under the Mortgage and Deed of Trust,
dated as of June 1, 1939, as amended and supplemented (the "Mortgage"), from the
Company to Citibank, N.A., as trustee, (2) unsecured debt securities (the
"Unsecured Debt Securities", and, together with the Secured Debt Securities, the
"Debt Securities") under the Indenture, dated as of April 1, 1998 (the
"Indenture"), from the Company to The Bank of New York, as successor trustee,
(3) shares of the Company's Preferred Stock, cumulative, no par value (the "New
Preferred Shares"), (4) shares of the Company's common stock, no par value (the
"New Common Shares"), to be issued and sold from time to time by the Company in
one or more public offerings. The New Common Shares will be offered and issued
together with the related preferred share purchase rights (the "New Rights") in
accordance with the Rights Agreement, dated as of November 15, 1999 (the "Rights
Agreement"), between the Company and The Bank of New York, as rights agent.

      We have examined (1) the Registration Statement, (2) the Company's
Restated Articles of Incorporation, as amended, and By-Laws, (3) a Certificate
of Existence/Authorization with respect to the Company issued by the Secretary
of State of the State of Washington, (4) the Mortgage, (5) the Indenture, (6)
the Rights Agreement, (7) orders of the Washington Utilities and Transportation
Commission (the "WUTC"), the Idaho Public Utilities Commission (the "IPUC") and
the Public Utility Commission of Oregon (the "OPUC") authorizing the issuance
and sale by the Company of the New Common Shares, as well as the exemptive order
of the Public Service Commission of the State of Montana disclaiming
jurisdiction over the issuance of securities and the creation of liens by the
Company and (8) various corporate records and other documents relating to the
authorization of the issuance and sale by the Company of securities. We have
also examined such other documents and satisfied ourselves as to such other
matters as we have deemed necessary in order to deliver this letter.

      On the basis of the foregoing, and subject to the qualifications
hereinafter expressed, we are of the opinion that:

    NEW YORK  WASHINGTON, D.C.  LOS ANGELES  EAST PALO ALTO  HOUSTON  AUSTIN
                LONDON  WARSAW  FRANKFURT  MILAN  ROME  BEIJING



Avista Corporation
December 11, 2006
Page 2

            (1) when (a) the WUTC, the IPUC and the OPUC have issued appropriate
      orders authorizing the issuance and sale by the Company of the Debt
      Securities and (b) the Debt Securities have been issued, sold and paid for
      as contemplated in the Registration Statement, the Debt Securities will be
      legally issued and will be binding obligations of the Company, except as
      limited by laws and principles of equity relating to or affecting
      generally the enforcement of mortgagees' and other creditors' rights
      including, without limitation, bankruptcy and insolvency laws (such laws
      and principles of equity being hereinafter called, collectively, the
      "Exceptions");

            (2) when (a) the WUTC, the IPUC and the OPUC have issued appropriate
      orders authorizing the issuance and sale by the Company of the New
      Preferred Shares and (b) the New Preferred Shares have been issued, sold
      and paid for as contemplated in the Registration Statement, the New
      Preferred Shares will be legally issued, fully paid and non-assessable;
      and

            (3) when the New Common Shares are issued and delivered as
      contemplated in the Registration Statement, the New Common Shares will be
      legally issued, fully paid and non-assessable and the New Rights will be
      legally issued and binding obligations, except as may be limited by the
      Exceptions.

      It is also our opinion that Section 23B.06.240 of the Washington Business
Corporation Act permits Washington corporations to enter into shareholder rights
plans, such as the Rights Agreement, and to issue rights thereunder, such as the
New Rights. However, we are not aware of any court decisions applying Washington
law that address the validity of actions taken by the board of directors of a
Washington corporation in authorizing a shareholder rights plan or the issuance
of rights thereunder.

      In our view, it is reasonable to assume, and we do assume, that a court
applying the law of the State of Washington, when presented with questions
concerning matters such as the authorization and issuance of the New Rights,
after giving effect to the "business judgment rule" under Washington statutory
and case law, most likely would look to and apply the corporation law of the
State of Delaware for guidance and authority. Accordingly, our opinion relating
to the legal issuance of the New Rights is based, in part, upon such assumption.

      For the purposes of the opinions expressed above, we have assumed that the
Debt Securities, the New Preferred Shares, the New Common Shares and the New
Rights will be issued and sold in compliance with the orders of the WUTC, the
IPUC and the OPUC authorizing the issuance and sale by the Company of such
securities and with the authorization of the Company's Board of Directors.

      To the extent that the opinions expressed above relate to or are dependent
upon matters governed by the law of the State of Washington, Idaho, Montana or
Oregon, we have relied upon the opinions expressed in the letter of even date
herewith of Marian M. Durkin, Esq., Senior Vice President and General Counsel,
which is being filed as Exhibit 5(a) to the Registration Statement, and our
opinions are subject to the same assumption, limitations and qualifications with
respect to such matters as are set forth in such letter.



Avista Corporation
December 11, 2006
Page 3

      Marian M. Durkin, Esq. is authorized to rely upon the opinions expressed
in this letter as to all matters governed by the federal securities laws, the
Federal Power Act, as amended, or the Public Utility Holding Company Act of
2005.

      We hereby consent to the filing of this letter as Exhibit 5(b) to the
Registration Statement and to the references to our firm, as counsel, in the
Registration Statement and in the prospectus contained therein. In giving the
foregoing consent, we do not admit that we are within the category of persons
whose consent is required under Section 7 of the Act or the rules and
regulations promulgated thereunder.

                                     Very truly yours,

                                     /s/ Dewey Ballantine LLP

                                     DEWEY BALLANTINE LLP