EXHIBIT 4.6

              CREDIT SUISSE FIRST BOSTON MORTGAGE SECURITIES CORP.
                                    Depositor

          Commercial Mortgage Pass-Through Certificates, Series 2006-C1

                             UNDERWRITING AGREEMENT
                             ----------------------

                                                                   March 7, 2006

CREDIT SUISSE SECURITIES (USA) LLC
Eleven Madison Avenue
New York, New York  10010

MCDONALD INVESTMENTS INC.
127 Public Square
Cleveland, Ohio 44114

GMAC COMMERCIAL HOLDING CAPITAL MARKETS CORP.
200 Witmer Road
Horsham, Pennsylvania  19044

BANC OF AMERICA SECURITIES LLC
214 North Tryon Street
NC1-027-22-03
Charlotte, North Carolina  28255

Ladies and Gentlemen:

      1. Introductory. Credit Suisse First Boston Mortgage Securities Corp., a
Delaware corporation (the "Depositor"), proposes to form one or more real estate
mortgage investment conduits (the "Trust"), which will issue securities entitled
Credit Suisse First Boston Mortgage Securities Corp. Commercial Mortgage
Pass-Through Certificates, (the "Certificates"), Series 2006-C1. Each
Certificate will evidence a fractional undivided, percentage interest or
beneficial interest in the Trust. The terms on which the Trust will issue the
Certificates will be specified in the Prospectus (as defined herein). The
property of the Trust will consist of a pool of 471 fixed rate mortgage loans,
secured by 527 multifamily and commercial properties (collectively, the
"Mortgage Loans") that will be purchased by the Depositor from Column Financial,
Inc. (the "Column Mortgage Loan Seller"), GMAC Commercial Mortgage Corporation
(the "GMAC Mortgage Loan Seller"), KeyBank National Association (the "KeyBank
Mortgage Loan Seller") and NCB, FSB (the "NCB, FSB Mortgage Loan Seller" and
together with the Column Mortgage Loan Seller, the KeyBank Mortgage Loan Seller
and the GMAC Mortgage Loan Seller, the "Mortgage Loan Sellers"), pursuant to
those certain Mortgage Loan Purchase Agreements, each dated as of March 1, 2006
(the "Mortgage Loan Purchase Agreements"), and will be serviced by GMAC
Commercial Mortgage Corporation, KeyCorp Real Estate Capital Markets, Inc. and
NCB, FSB, each as a Master Servicer of their respective group of Mortgage Loans
as set forth in the Pooling and Servicing Agreement (defined below)
(collectively the "Master Servicers"), and if and when necessary GMAC Commercial
Mortgage Corporation or National Consumer Cooperative Bank as Special Servicer
of their respective group of mortgage loans as set forth in the Pooling and
Servicing Agreement (collectively the "Special Servicers"), pursuant to that
certain Pooling and Servicing Agreement (the "Pooling and Servicing Agreement"),
to be dated as of March 1, 2006, by and among the Depositor, the Master
Servicers, the Special Servicers and Wells Fargo Bank, N.A., as trustee (the
"Trustee"), and certain related property to be conveyed to the Trust by the
Depositor (the "Trust Fund"). The Mortgage Loans will be transferred to the
Trust, and the Certificates will be issued pursuant to the Pooling and Servicing
Agreement.

      The offering of the Certificates made pursuant to the Registration
Statement (as defined below) will be made through you as underwriters. This
Agreement provides for the sale of such Certificates to, and the purchase and
offering thereof by, you, as underwriters (the "Underwriters" and, individually,
an "Underwriter"). Schedule I shall specify the principal or notional balance of
each Class of the Certificates to be issued and any terms thereof not otherwise
specified in the Pooling and Servicing Agreement, the Classes of Certificates
subject to this Agreement, the price at which such Certificates are to be
purchased by the Underwriters from the Depositor, the aggregate amount of
Certificates to be purchased by you and the initial public offering price or the
method by which the price at which such Certificates are to be sold will be
determined. The offering of the Certificates will be governed by this Agreement.

      At or prior to the time when sales to purchasers of the Certificates were
first made, which was approximately 1:30 p.m. on March 7, 2006 (the "Time of
Sale"), the Depositor had prepared the following information (collectively, the
"Rule 159 Information"): the Depositor's Free Writing Prospectus dated February
24, 2006 (the cover page of which is attached hereto as Annex A) to the
Depositor's Prospectus dated February 24, 2006, and the Depositor's Prospectus
dated February 24, 2006, the term sheet dated February 24, 2006, relating to the
Certificates, and each "free-writing prospectus" (as defined pursuant to Rule
405 under the 1933 Act) (a "Free Writing Prospectus") the first page of each of
which is attached as Annex B hereto. If, subsequent to the date of this
Agreement, the Depositor and the Underwriters determine that such information
included an untrue statement of material fact or omitted to state a material
fact necessary in order to make the statements therein, in the light of the
circumstances under which they were made, not misleading and terminate their old
purchase contracts and enter into new purchase contracts with investors in the
Certificates, then "Rule 159 Information" will refer to the information conveyed
to purchasers at the time of entry into the first such new purchase contract,
including any information that corrects such material misstatements or omissions
("Corrective Information") and "Time of Sale" will refer to the time and date on
which such new purchase contracts were entered into.

      2. Representations and Warranties of the Depositor.

      The Depositor represents and warrants to you as of the date hereof as
follows:

      (a) The Depositor has filed with the Securities and Exchange Commission
(the "Commission") a registration statement (No. 333-129918) on Form S-3 for the
registration of the Certificates under the Securities Act of 1933, as amended
(the "1933 Act"), which registration statement has become effective. The
Depositor proposes to file with the Commission pursuant to Rule 424(b) under the
1933 Act a supplement to the form of prospectus included in such registration
statement relating to the Certificates and the plan of distribution thereof.
Such registration statement, including the exhibits thereto and information that
is contained in the Prospectus (as defined below) and is deemed to be part of
and included in such registration statement, as such registration statement may
have been amended or supplemented at the date of the Prospectus, and including
the Prospectus, is hereinafter referred to as the "Registration Statement"; the
prospectus first required to be filed to satisfy the condition set forth in Rule
172(c) and pursuant to Rule 424(b) under the 1933 Act, is hereinafter referred
to as the "Base Prospectus"; such form of supplement to the Base Prospectus
relating to the Certificates, in the form first required to be filed to satisfy
the condition set forth in Rule 172(c) and pursuant to Rule 424(b) under the
1933 Act (including the Base Prospectus as so supplemented) is hereinafter
referred to as the "Prospectus Supplement"; and the Base Prospectus and the
Prospectus Supplement, together, are hereinafter referred to as the
"Prospectus." The conditions to the use of a registration statement on Form S-3
under the Act, as set forth in the General Instructions to Form S-3, and the
conditions of Rule 415 under the Act have been satisfied with respect to the
Registration Statement; and no other amendment to the Registration Statement
will be filed which shall have been reasonably disapproved by you promptly after
reasonable notice thereof. There is no request by the Commission for any further
amendment of the Registration Statement or the Prospectus or for any additional
information; the Commission has not issued any stop order suspending the
effectiveness of the Registration Statement and the Depositor is not aware of
any proceeding for that purpose having been instituted or threatened; and there
has been no notification with respect to the suspension of the qualification for
sale of the Certificates for sale in any jurisdiction or any proceeding for such
purpose having been instituted or threatened;

      (b) the Registration Statement (i) on its effective date and on the date
of the then most recently filed Prospectus Supplement conformed in all respects
to the requirements of the 1933 Act and the rules and regulations thereunder
(the "Rules and Regulations") and did not include any untrue statement of a
material fact or omit to state any material fact required to be stated therein
or necessary to make the statements therein not misleading and (ii) on the date
hereof will conform in all respects to the requirements of the 1933 Act and the
Rules and Regulations thereunder and will not include any untrue statement of a
material fact or omit to state any material fact required to be stated therein
or necessary to make the statements therein not misleading and the Prospectus on
the date hereof and on the Specified Delivery Date (as defined in Section 3
hereof) will conform in all respects to the requirements of the 1933 Act and the
Rules and Regulations thereunder and will not include any untrue statement of a
material fact or omit to state any material fact required to be stated therein
or necessary to make the statements therein, in the light of the circumstances
under which they were made, not misleading; provided, however, that the
foregoing does not apply to statements in or omissions from either the
Registration Statement or the Prospectus to the extent based upon and in
conformity with (A) written information furnished to the Depositor by any
Underwriter specifically for use therein (the "Underwriter Information"), and
(B) the Mortgage Loan Seller's Information (collectively as defined in each of
the Indemnification Agreements, dated as of the date hereof (the
"Indemnification Agreements"), by and among the Depositor, each Mortgage Loan
Seller and each Underwriter);

      (c) There is no request by the Commission for any further amendment of the
Registration Statement or the Prospectus or for any additional information; the
Commission has not issued any stop order suspending the effectiveness of the
Registration Statement and the Depositor is not aware of any proceeding for that
purpose having been instituted or threatened; and there has been no notification
with respect to the suspension of the qualification for sale of the Certificates
for sale in any jurisdiction or any proceeding for such purpose having been
instituted or threatened;

      (d) The Rule 159 Information, at the Time of Sale, did not, and at the
Closing Date will not, contain any untrue statement of a material fact or omit
to state a material fact necessary in order to make the statements therein, in
the light of the circumstances under which they were made, not misleading;
provided that the Depositor makes no representation and warranty with respect to
(A) any statements or omissions made in reliance upon and in conformity with the
Underwriter Information or (B) any Mortgage Loan Seller Information contained in
or omitted from such Time of Sale Information. The parties acknowledge that none
of the Underwriters has furnished any Underwriter Information to the Depositor
expressly for use in the Rule 159 Information.

      (e) Other than the Prospectus, the Depositor (including its agents and
representatives other than the Underwriters in their capacity as such) has not
made, used, prepared, authorized, approved or referred to and will not make,
use, prepare, authorize, approve or refer to any "written communication" (as
defined in Rule 405 under the 1933 Act) that constitutes an offer to sell or
solicitation of an offer to buy the Certificates other than (i) any document not
constituting a prospectus pursuant to Section 2(a)(10)(a) of the 1933 Act or
Rule 134 under the 1933 Act, (ii) the Rule 159 Information, and (iii) each other
written communication of the Depositor or its agents and representatives
approved by the Underwriters either in writing in advance or in any other manner
mutually agreed by the Underwriters and the Depositor (each such communication
referred to in clause (ii) and this clause (iii) constituting an Issuer Free
Writing Prospectus (as defined in Section 8(b) hereof). Each such Issuer Free
Writing Prospectus complied or, if used after the date hereof, will comply, in
all material respects with the 1933 Act and the rules and regulations
promulgated thereunder, has been filed or will be filed in accordance with
Section 8 (to the extent required thereby) and did not at the Time of Sale, and
at the Closing Date will not, contain any untrue statements of a material fact
or (when read in conjunction with the other Rule 159 Information) omit to state
a material fact necessary in order to make the statements therein, in the light
of the circumstances under which they were made, not misleading; provided that
the Depositor makes no representation and warranty with respect to (i) any
statements or omissions made in reliance upon and in conformity with the
Underwriter Information or (ii) any Mortgage Loan Seller Information contained
in or omitted from any Issuer Free Writing Prospectus. The parties acknowledge
that none of the Underwriters has furnished any Underwriter Information to the
Depositor expressly for use in any Issuer Free Writing Prospectus.

      (f) the Depositor has been duly organized and is validly existing as a
corporation in good standing under the laws of the State of Delaware, with full
corporate power and authority to own its assets and conduct its business as
described in the Prospectus, is duly qualified as a foreign corporation in good
standing in all jurisdictions in which the ownership or lease of its property or
the conduct of its business requires such qualification, except where the
failure to be so qualified would not have a material adverse effect on the
Depositor, and is conducting its business so as to comply in all material
respects with the applicable statutes, ordinances, rules and regulations of the
jurisdictions in which it is conducting business;

      (g) the Pooling and Servicing Agreement, the Mortgage Loan Purchase
Agreements and the Certificates conform, or will conform as of the Specified
Delivery Date, to the description thereof contained in the Registration
Statement and the Prospectus; and the Certificates, on the date hereof, will
have been duly and validly authorized and, when such Certificates are duly and
validly executed by the Depositor or the Trustee, authenticated by the Trustee
and delivered in accordance with the Pooling and Servicing Agreement and
delivered and paid for as provided herein, will be validly issued and
outstanding and entitled to the benefits afforded by the Pooling and Servicing
Agreement;

      (h) the Depositor is not in violation of its certificate of incorporation
or by-laws or in default under any agreement, indenture or instrument the effect
of which violation or default would be material and adverse to the Depositor or
which violation or default would have a material adverse effect on the
performance by the Depositor of its obligations under this Agreement, the
Pooling and Servicing Agreement, the Certificates or any of the Mortgage Loan
Purchase Agreements; there are no actions or proceedings against, or
investigations of, the Depositor pending, or, to the knowledge of the Depositor,
threatened, before any court, administrative agency or other tribunal (i)
asserting the invalidity of this Agreement, the Pooling and Servicing Agreement,
any of the Mortgage Loan Purchase Agreements or the Certificates, (ii) seeking
to prevent the issuance of the Certificates or the consummation of any of the
transactions contemplated by this Agreement, (iii) which might materially and
adversely affect the performance by the Depositor of its obligations under, or
the validity or enforceability against the Depositor of, this Agreement, the
Pooling and Servicing Agreement, any of the Mortgage Loan Purchase Agreements or
the Certificates or (iv) seeking to affect adversely the federal income tax
attributes of the Certificates described in the Prospectus;

      (i) there has not been, and as of the Specified Delivery Date there will
not be, any material adverse change in the business operations, financial
condition, properties or assets of the Depositor since the date of its latest
audited financial statements which would have a material adverse effect on the
ability of the Depositor to perform its obligations under this Agreement, the
Pooling and Servicing Agreement or any of the Mortgage Loan Purchase Agreements;

      (j) there are no contracts, indentures or other documents of a character
required by the 1933 Act or by the rules and regulations thereunder to be
described or referred to in the Registration Statement or the Prospectus or to
be filed as exhibits to the Registration Statement which have not been so
described or referred to therein or so filed or incorporated by reference as
exhibits thereto;

      (k) the Depositor possesses all material licenses, certificates,
authorizations or permits issued by the appropriate state, federal or foreign
regulatory agencies or bodies necessary to conduct the business now operated by
it, and the Depositor has not received any notice of proceedings relating to the
revocation or modification of any such license, certificate, authorization or
permit which, singly or in the aggregate, if the subject of any unfavorable
decision, ruling or finding, would materially and adversely affect the
condition, financial or otherwise, or the earnings, business affairs or business
prospects of the Depositor;

      (l) the issue and sale of the Certificates and the compliance by the
Depositor with all of the provisions of the Certificates, each Mortgage Loan
Purchase Agreement, this Agreement and the Pooling and Servicing Agreement, and
the execution and delivery by the Depositor of this Agreement, the Pooling and
Servicing Agreement and the Mortgage Loan Purchase Agreements are within the
corporate power of the Depositor and have been, or will have been, duly
authorized by all necessary corporate action on the part of the Depositor; and
neither the execution and delivery by the Depositor of such instruments, nor the
consummation by the Depositor of the transactions herein or therein
contemplated, nor the compliance by the Depositor with the provisions hereof or
thereof, will (A) conflict with or result in a breach of, or constitute a
default under, any of the provisions of the certificate of incorporation or
by-laws of the Depositor, (B) conflict with any of the provisions of any law,
governmental rule, regulation, judgment, decree or order binding on the
Depositor or its properties, (C) conflict with any of the provisions of any
indenture, mortgage, contract or other instrument to which the Depositor is a
party or by which it is bound or (D) except as contemplated by the Pooling and
Servicing Agreement, result in the creation or imposition of any lien, charge or
encumbrance upon any of its property or assets pursuant to the terms of any such
indenture, mortgage, contract or other instrument;

      (m) this Agreement has been duly authorized, executed and delivered by the
Depositor;

      (n) on the Specified Delivery Date, the Pooling and Servicing Agreement
and the Mortgage Loan Purchase Agreements will have been duly authorized,
executed and delivered by the Depositor and will be valid and binding agreements
of the Depositor, enforceable against the Depositor in accordance with their
respective terms, except to the extent that enforcement thereof may be limited
by (1) bankruptcy, insolvency, reorganization, moratorium or other similar laws
now or hereafter in effect relating to creditors' rights generally and (2)
general principles of equity (regardless of whether enforceability is considered
in a proceeding at law or in equity);

      (o) all approvals, authorizations, consents, orders or other actions of
any person, corporation or other organization, or of any court, governmental
agency or body or official (except with respect to the state securities or "blue
sky" laws of various jurisdictions) required in connection with the valid and
proper authorization, issuance and sale of the Certificates pursuant to this
Agreement and the Pooling and Servicing Agreement have been or will be taken or
obtained on or prior to the Specified Delivery Date;

      (p) at the Specified Delivery Date, each of the Mortgage Loans will meet
the criteria for selection described in the Prospectus Supplement;

      (q) neither the Depositor nor the Trust Fund is, and neither the sale of
the Certificates in the manner contemplated by the Prospectus nor the activities
of the Trust Fund pursuant to the Pooling and Servicing Agreement will cause the
Depositor or the Trust Fund to be an "investment company" or under the control
of an "investment company" as such terms are defined under the Investment
Company Act of 1940, as amended (the "Investment Company Act"), and the Pooling
and Servicing Agreement is not required to be qualified under the Trust
Indenture Act of 1939, as amended (the "Trust Indenture Act");

      (r) at the time of the execution and delivery of the Pooling and Servicing
Agreement, the Depositor (A) except as disclosed in the Prospectus, will convey
to the Trustee, or cause to be conveyed to the Trustee, all of the Depositor's
right, title and interest in and to the Mortgage Loans being transferred to the
Trustee pursuant to the Pooling and Servicing Agreement, free and clear of any
lien, mortgage, pledge, charge, encumbrance, adverse claim or other security
interest (collectively "Liens") granted by or imposed upon the Depositor, (B)
will not have assigned to any person any of its right, title or interest in the
Mortgage Loans or in the Pooling and Servicing Agreement or the Certificates,
and (C) will have the power and authority to transfer or cause to be transferred
the Mortgage Loans to the Trustee and to sell the Certificates to the
Underwriters. Upon execution and delivery of the Pooling and Servicing Agreement
by the Trustee, the Trustee will have acquired ownership of all of the
Depositor's right, title and interest in and to the Mortgage Loans except to the
extent disclosed in the Prospectus, and upon delivery to the Underwriters of the
Certificates pursuant hereto, each Underwriter will have good title to the
Certificates purchased by such Underwriter, in each case free of Liens granted
by or imposed upon the Depositor;

      (s) under generally accepted accounting principles and for federal income
tax purposes, the Depositor will report the transfer of the Mortgage Loans to
the Trustee in exchange for the Certificates and the sale of the Certificates to
the Underwriters pursuant to this Agreement as a sale of the interest in the
Mortgage Loans evidenced by the Certificates. The consideration received by the
Depositor upon the sale of the Certificates to the Underwriters will constitute
reasonably equivalent value and fair consideration for the Certificates. The
Depositor will be solvent at all relevant times prior to, and will not be
rendered insolvent by, the sale of the Certificates to the Underwriters. The
Depositor is not selling the Certificates to the Underwriters with any intent to
hinder, delay or defraud any of the creditors of the Depositor;

      (t) at the Specified Delivery Date, the respective Classes of Certificates
shall have been assigned ratings no lower than those set forth in Schedule I
hereto by the nationally recognized statistical rating organizations identified
in Schedule I hereto;

      (u) any taxes, fees and other governmental charges in connection with the
execution, delivery and issuance of this Agreement, the Pooling and Servicing
Agreement and the Certificates payable by the Depositor (other than income
taxes) have been paid or will be paid at or prior to the Specified Delivery
Date; and

      (v) the Depositor is not, and on the date on which the first bona fide
offer of the Certificates is made will not be, an "ineligible issuer," as
defined in Rule 405 under the 1933 Act.

      3. Purchase, Sale and Delivery of Certificates. Delivery of and payment
for the Certificates will be made at such place and at such time as shall be
specified in Schedule I or at such other time thereafter as set forth in
Schedule I or as you and the Depositor shall agree upon, each such time being
hereinafter referred to as a "Specified Delivery Date." Delivery of such
Certificates shall be made by the Depositor to the Underwriters against payment
of the purchase price specified in Schedule I in same day funds wired to such
bank as may be designated by the Depositor, or by such other manner of payment
as may be agreed upon by the Depositor and you. Unless otherwise provided for,
the Certificates to be so delivered will be in definitive, fully registered
form, in such denominations and registered in such names as you request, and
will be made available through the facilities of The Depository Trust Company,
or otherwise as you may request.

      4. Offering by Underwriters.

      (a) It is understood that the Underwriters propose to offer the
Certificates subject to this Agreement for sale to the public as set forth in
the Prospectus.

      (b) Each Underwriter represents, warrants and agrees that: (i) it has not
sold or offered the Certificates in the United Kingdom, and it has not delivered
or communicated the Prospectus or any other invitation or inducement to buy or
participate in the Certificates in the United Kingdom, except to persons who (A)
have professional experience of participating in unregulated collective
investment schemes and of matters relating to investments falling within both
Article 14(5) of the Financial Services and Markets Act 2000 (Promotion of
Collective Investment Schemes) (Exemptions) Order 2001 (the "CIS Order") and
Article 19(5) of the Financial Services and Markets Act (Financial Promotion)
Order 2001 (the "FP order") or (B) fall within Article 22(2)(a) through (d)
("high net worth companies, unincorporated associations, etc.") of the CIS Order
and Article 49(2)(a) though (d) of the FP Order; and (ii) it has complied and
will comply with all applicable provisions of the Financial Services and Markets
Act 2000 with respect to anything done by it in relation to the Certificates in,
from or otherwise involving the United Kingdom.

      5. Covenants of the Depositor. The Depositor covenants and agrees with you
that:

      (a) the Depositor has prepared and/or shall prepare a Prospectus
Supplement setting forth the amount of Certificates covered thereby and the
terms thereof not otherwise specified in the Base Prospectus, the price at which
such Certificates are to be purchased by the Underwriters from the Depositor,
either the initial public offering price or the method by which the price at
which such Certificates are to be sold will be determined, the selling
concessions and reallowances, if any, and such other information as you and the
Depositor deem appropriate in connection with the offering of such Certificates,
but the Depositor shall not file any amendments to the Registration Statement as
in effect with respect to the Certificates, or any amendments or supplements to
the Prospectus, unless it has first delivered copies of such amendments or
supplements to you and given you a reasonable opportunity to review the same or
if you have reasonably objected thereto promptly after receipt thereof; the
Depositor shall immediately advise you or your counsel (i) when notice is
received from the Commission that any post-effective amendment to the
Registration Statement has been filed or has become or will become effective or
any supplement to the Prospectus or any amended Prospectus, in each case
relating to the Certificates specified in Schedule I has been filed and will
furnish you with copies thereof, (ii) of any request by the Commission for any
amendment of the Registration Statement or the Prospectus or for any additional
information relating to the Certificates and (iii) of any order or communication
suspending or preventing, or threatening to suspend or prevent, the offer and
sale of the Certificates or of any proceedings or examinations that may lead to
such an order or communication, whether by or of the Commission or any authority
administering any state securities or "blue sky" law, as soon as the Depositor
is advised thereof, and shall use its best efforts to prevent the issuance of
any such order or communication and to obtain as soon as possible its lifting,
if issued;

      (b) if, at any time when the Prospectus is required to be delivered under
the 1933 Act, any event occurs as a result of which the Prospectus as then
amended or supplemented would include any untrue statement of a material fact or
omit to state any material fact necessary to make the statements therein, in
light of the circumstances under which they were made, not misleading, or if it
is necessary at any time to amend or supplement the Prospectus to comply with
the 1933 Act or the Rules and Regulations, the Depositor shall prepare and file
with the Commission, an amendment or supplement that will correct such statement
or omission or an amendment that will effect such compliance;

      (c) the Depositor shall make generally available to the holders of the
Certificates (the "Certificateholders"), in each case as soon as practicable,
earning statements covering (i) a period of 12 months beginning not later than
the first day of the related Trust's fiscal quarter next following the effective
date of the Registration Statement and (ii) a period of 12 months beginning no
later than the first day of the Trust's fiscal quarter next following the date
hereof which will satisfy the provisions of Section 11(a) of the 1933 Act and
Rule 158 of the Commission with respect to the Certificates. The Depositor shall
cause the Trustee to furnish or make available, within a reasonable time after
the end of each calendar year, to each holder of a Certificate at any time
during such year, such information as the Depositor deems necessary or desirable
to assist Certificateholders in preparing their federal income tax returns;

      (d) the Depositor shall furnish to you copies of the Registration
Statement, the Prospectus, and all amendments and supplements to such documents
relating to the Certificates, in each case as soon as available and in such
quantities as you reasonably request as long as the Depositor is required to
deliver the Prospectus under the 1933 Act in connection with the sale of the
Certificates; provided that any such documents requested by you on a date that
is more than nine (9) months after March 22, 2006 (the "Closing Date") shall be
provided at your expense;

      (e) the Depositor shall arrange for the qualification of the Certificates
for sale and the determination of their eligibility for investment under the
laws of such jurisdictions as you designate and shall continue such
qualifications in effect so long as required for the distribution; provided,
however, that neither the Depositor nor the Trust shall be required to qualify
to do business in any jurisdiction where it is now not qualified or to take any
action which would subject it to general or unlimited service of process in any
jurisdiction in which it is now not subject to service of process;

      (f) the Depositor shall, while the Certificates are outstanding;

            (i) furnish to you, as soon as available, copies of all reports
filed with the Commission and copies of each notice published or mailed to
holders of the Certificates pursuant to the Pooling and Servicing Agreement; and

            (ii) furnish to you such other information with respect to the Trust
or its financial condition or results of operations, as you may reasonably
request, including but not limited to information necessary or appropriate to
the maintenance of a secondary market in the Certificates; and

      (g) as between itself and the Underwriters, the Depositor will pay all
expenses incidental to the performance of its obligations under this Agreement,
including without limitation (i) expenses of preparing, printing and reproducing
the Prospectus (including any amendments thereof and supplements thereto), the
Pooling and Servicing Agreement and the Certificates, (ii) the fees charged by
Fitch Ratings, Inc, ("Fitch") and Standard & Poor's Ratings Services, a division
of The McGraw-Hill Companies, Inc. ("S&P" and together with Fitch, the "Rating
Agencies") for rating the Certificates, (iii) the fees and expenses of the
Trustee, and any agent of the Trustee and the fees and disbursements of counsel
for the Trustee in connection with the Pooling and Servicing Agreement and the
Certificates, and (iv) all other costs and expenses incidental to the
performance by the Depositor of its obligations hereunder that are not otherwise
specifically provided for in this subsection. It is understood that, except as
provided in this subsection (g) and in Section 10 below, each Underwriter will
pay all of its own expenses including all out-of-pocket and/or internally
allocated costs and expenses incurred by them in connection with the transaction
herein contemplated, including, without limitation, fees and expenses of their
counsel, any transfer taxes on the Certificates and the expenses of any
advertising of the offering of the Certificates made by the Underwriters; and

      (h) during the period when a prospectus is required by law to be delivered
in connection with the sale of the Certificates pursuant to this Agreement, the
Depositor shall file, or cause the Trustee to file on behalf of the Trust, on a
timely and complete basis, all documents that are required to be filed by the
related Trust with the Commission pursuant to Sections 13, 14 or 15(d) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act").

      6. Conditions to the Obligations of the Underwriters. The obligations of
the Underwriters to purchase and pay for the Certificates subject to this
Agreement will be subject to the accuracy of the representations and warranties
on the part of the Depositor as of the date hereof and the Specified Delivery
Date, to the accuracy of the statements of the Depositor made pursuant to the
provisions hereof, to the performance by the Depositor in all material respects
of its obligations hereunder and to the following additional conditions
precedent:

      (a) you shall have received a letter from Ernst & Young LLP dated the date
hereof and, if requested by you, dated the Specified Delivery Date, each in the
forms heretofore agreed to;

      (b) all actions required to be taken and all filings required to be made
by the Depositor under the 1933 Act prior to the Specified Delivery Date shall
have been duly taken or made; and prior to the Specified Delivery Date, no stop
order suspending the effectiveness of the Registration Statement shall have been
issued and no proceedings for that purpose shall have been instituted, or to the
knowledge of the Depositor or any Underwriter, shall be contemplated by the
Commission;

      (c) unless otherwise specified in Schedule I, the Certificates subject to
this Agreement and offered by means of the Registration Statement shall be rated
the ratings specified in Schedule I, and shall not have been lowered or placed
on any credit watch with a negative implication for downgrade;

      (d) you shall have received an opinion of counsel to the guarantor, Credit
Suisse acting through Credit Suisse USA Inc. dated the Specified Delivery Date,
and in the form agreed to on or prior to such date;

      (e) you shall have received opinions of Cadwalader, Wickersham & Taft LLP,
special counsel to the Depositor and Credit Suisse Securities (USA) LLC, dated
the Specified Delivery Date, in substantially the form agreed to on or prior to
such date;

      (f) you shall have received an opinion of special counsel to each Mortgage
Loan Seller, dated the Specified Delivery Date, in the form agreed to on or
prior to such date;

      (g) you shall have received an opinion of counsel to the Trustee, dated
the Specified Delivery Date, which shall be dated the date of the Mortgage Loan
Purchase Agreements, in the form agreed to on or prior to such date, together
with a reliance letter addressed to the Rating Agencies, the Depositor and the
Trustee;

      (h) you shall have received an opinion of counsel of each Master Servicer,
dated the Specified Delivery Date, in the form agreed to on or prior to such
date;

      (i) you shall have received an opinion of counsel of each Special
Servicers, dated the Specified Delivery Date, in the form agreed to on or prior
to such date

      (j) you shall have received letters, dated the Specified Delivery Date,
from counsel rendering opinions to the Rating Agencies, to the effect that you
may rely upon their opinion to such Rating Agencies, as if such opinion were
rendered to you, or such opinions shall be addressed to you;

      (k) you shall have received a certificate or certificates signed by such
of the principal executive, financial and accounting officers of the Depositor
as you may request, dated the Specified Delivery Date, in the form agreed to on
or prior to such date;

      (l) you shall have received a certificate of the Trustee, signed by one or
more duly authorized officers of the Trustee, dated the Specified Delivery Date,
in the form agreed to on or prior to such date;

      (m) you shall have received a certificate of each Master Servicer, signed
by one or more duly authorized officers of such Master Servicer, dated the
Specified Delivery Date, in the form agreed to on or prior to such date;

      (n) you shall have received a certificate of each Special Servicer, signed
by one or more duly authorized officers of such Special Servicer, dated the
Specified Delivery Date, in the form agreed to on or prior to such date;

      (o) the Mortgage Loan Sellers shall have sold the Mortgage Loans to the
Depositor pursuant to the Mortgage Loan Purchase Agreements; and

      (p) you shall have received such other documents, certificates, letters
and opinions as you may reasonably request.

      7. Indemnification.

      (a) The Depositor shall indemnify and hold harmless each Underwriter, each
of its officers and each of its directors and each person, if any, that controls
any Underwriter within the meaning of the 1933 Act or the Exchange Act against
any expenses, losses, claims, damages or liabilities, joint or several, to which
such Underwriter or such officer, director or controlling person may become
subject under the 1933 Act, the Exchange Act or otherwise, and shall reimburse
any legal or other expenses reasonably incurred by such Underwriter or any such
director, officer, or controlling person in connection with investigating or
defending any such expense, loss, claim, damage, liability or action, in each
case insofar as such expenses, losses, claims, damages or liabilities (or
actions in respect thereof) arise out of or are based upon (i) any untrue
statement or alleged untrue statement of any material fact contained in the
Registration Statement or any amendment or supplement thereto or the omission or
alleged omission to state therein a material fact required to be stated therein
or necessary to make the statements therein not misleading, (ii) any untrue
statement or alleged untrue statement of any material fact contained in (x) any
Issuer Free Writing Prospectus or (y) any "Issuer Information," as defined in
Section 8(b) contained in (1) any Underwriter Free Writing Prospectus (as
defined in Section 8(b) hereof) prepared by or on behalf of such Underwriter, or
(2) any Free Writing Prospectus that is required to be filed pursuant to Section
8(e)(iii) or Section 8(h) hereof (clauses (x) and (y) collectively, the "Issuer
Disclosure Materials"), or the omission or alleged omission to state a material
fact required to make the statements therein (when read in connection with the
other Rule 159 Information), in light of the circumstances under which they were
made, not misleading, which error or omission was not corrected by information
subsequently supplied by the Depositor to such Underwriter within a reasonable
period of time prior to the Time of Sale or (iii) any breach of the
representation and warranty in Section 2(u). Notwithstanding the foregoing, (i)
the Depositor shall not be liable in any such case to the extent that any such
expense, loss, claim, damage or liability arises out of or is based upon any
such untrue statement or alleged untrue statement in, or omission or alleged
omission from, any such documents in reliance upon and in conformity with (A)
the Underwriter Information, (B) information regarding the Mortgage Loans that
is contained in the "Loan Detail" (as defined below) or, to the extent
consistent therewith, the Diskette; (C) information regarding any Mortgage Loan
Seller, the Mortgage Loans sold by such Mortgage Loan Seller to the Depositor or
the related mortgaged properties to the extent such information is covered by
the related Mortgage Loan Seller's Indemnification Agreement (the information in
clauses (B) and (C) referred to herein as the "Mortgage Loan Sellers'
Information"); or (D) information regarding the Trustee, the Master Servicers or
the Special Servicers contained in the Prospectus Supplement under the headings
"The Series 2006-C1 Pooling and Servicing Agreement--The Master Servicers,"
"--The Special Servicers," and "--The Trustee" and other sections but in each
only to the extent such information is covered by such party's indemnification
of the Underwriters and is actually indemnified by such party and (ii) such
indemnity with respect to an untrue statement or omission of a material fact
made in any Issuer Disclosure Materials that are part of the initial Rule 159
Information shall not inure to the benefit of any Underwriter if information
that corrected any untrue statement or omission of a material fact was furnished
to the Underwriters at a reasonable time prior to the Time of Sale. "Loan
Detail" shall mean the information set forth in Annex A-1 and Annex A-2 to the
Prospectus Supplement. "Diskette" shall mean the information set forth on the
diskette attached to the Prospectus Supplement.

      (b) The Depositor acknowledges that the following statements constitute
the only Underwriters' Information furnished in writing by or on behalf of the
Underwriters for inclusion in the Prospectus: the sixth paragraph on the cover
of the Prospectus Supplement; the sub-heading "--Underwriter" in the section of
the Prospectus Supplement entitled "Summary of Prospectus Supplement--Relevant
Parties/Entities"; and the first sentence of the fourth paragraph, and the
second sentence of the fifth paragraph under the heading "Underwriting" in the
Prospectus Supplement. This indemnity agreement shall be in addition to any
liability which the Depositor may otherwise have.

      (c) Each Underwriter shall severally, and not jointly, indemnify and hold
harmless the Depositor, each of its directors, each of its officers who has
signed the Registration Statement and each person, if any, who controls the
Depositor within the meaning of the 1933 Act or the Exchange Act against any
expenses, losses, claims, damages or liabilities to which the Depositor or any
such director, officer or controlling person may become subject under the 1933
Act, the Exchange Act or otherwise, and shall reimburse any legal or other
expenses reasonably incurred by the Depositor or any such director, officer or
controlling person in connection with investigating or defending any such
expense, loss, claim, damage, liability or action, in each case insofar as such
expenses, losses, claims, damages or liabilities (or actions in respect thereof)
arise out of or are based upon (i) any untrue statement or alleged untrue
statements of a material fact, or omissions or alleged omissions to state a
material fact required to be stated therein or necessary to make the statements
therein, in light of the circumstances under which they were made, not
misleading in the Underwriter Information and (ii) untrue statements or alleged
untrue statements of a material fact in any Underwriter Free Writing Prospectus
(as defined in Section 8(b)) or omission or alleged omission to state in such
Underwriter Free Writing Prospectus a material fact necessary in order to make
the statements therein (when read in conjunction with the Rule 159 Information),
in light of the circumstances under which they were made, not misleading; except
that, in the case of clause (ii), no Underwriter shall be obligated so to
indemnify and hold harmless the Depositor (x) for any losses, claims, damages or
liabilities caused by any untrue statement, alleged untrue statement, omission
or alleged omission (including those of a quantitative nature) resulting from an
error or omission in any Mortgage Loan Seller's Information (as defined in each
of the Indemnification Agreements) provided by a Mortgage Loan Seller or an
error or omission in any information provided by a Master Servicer, Special
Servicer or the Trustee and used for purposes of preparing such Free Writing
Prospectus, which Mortgage Loan Seller's Information or information provided by
a Master Servicer, Special Servicer or the Trustee was not corrected by
information subsequently supplied by the Depositor or any Mortgage Loan Seller
or the Master Servicer, Special Servicer or Trustee within a reasonable period
of time prior to the Time of Sale; (y) for any losses, claims, damages or
liabilities caused by any untrue statement, alleged untrue statement, omission
or alleged omission (including those of a quantitative nature) resulting from an
error or omission in the Issuer Information (as defined in Section 7(a) hereof)
supplied by the Depositor or any Mortgage Loan Seller to the Underwriter, which
Issuer Information was not corrected by information subsequently supplied by the
Depositor or any Mortgage Loan Seller within a reasonable period of time prior
to the Time of Sale; or (z) to the extent that the Depositor is entitled to
indemnification or contribution therefor from any Mortgage Loan Seller, Trustee,
Master Servicer or Special Servicer pursuant to any Indemnification Agreement.
Notwithstanding the foregoing, the indemnity provided in clause (ii) in the
immediately preceding sentence will apply only if such misstatement or omission
was not also a misstatement or omission in the Rule 159 Information. This
indemnity agreement shall be in addition to any liability that such Underwriter
may otherwise have.

      (d) Promptly after receipt by an indemnified party under this Section 7 of
notice of the commencement of any action, such indemnified party shall, if a
claim in respect thereof is to be made against the indemnifying party under this
Section 7, notify the indemnifying party of the commencement thereof; but the
omission to so notify the indemnifying party shall not relieve it from any
liability which it may have to any indemnified party under Section 7 (a) and
(c), except to the extent that such omission to notify materially prejudices the
indemnifying party or relieve it from any liability that it may have other than
under this Agreement. In case any such action is brought against any indemnified
party, after such indemnifying party has been notified of the commencement
thereof, such indemnifying party shall be entitled to participate therein (at
its own expense), and, to the extent that it may wish, shall be entitled to
assume the defense thereof (jointly with any other indemnifying party similarly
notified) with counsel reasonably satisfactory to such indemnified party (which
shall not, except with the consent of the indemnified party, be counsel to the
indemnifying party), and after notice from the indemnifying party to such
indemnified party of its election to so assume the defense thereof, the
indemnifying party shall not be liable to such indemnified party under this
Section 7 for any legal or other expenses subsequently incurred by such
indemnified party in connection with the defense thereof other than reasonable
costs of investigation. In any such proceeding, any indemnified party shall have
the right to retain its own counsel, but the fees and expenses of such counsel
shall be at the expense of such indemnified party unless (i) the indemnifying
party and the indemnified party shall have agreed to the retention of such
counsel, (ii) the named parties to any such proceeding (including any impleaded
parties) include both the indemnifying party and the indemnified party and
representation of both parties by the same counsel would be inappropriate due to
actual or potential differing interests between them or (iii) the indemnifying
party shall have failed to designate within a reasonable period of time counsel
reasonably satisfactory to the indemnified party (in which case the fees and
expenses shall be paid by the indemnifying party as incurred by the indemnified
party). In no event shall the indemnifying parties be liable for fees and
expenses of more than one counsel (in addition to any local counsel) separate
from their own counsel for all indemnified parties in connection with any one
action or separate but similar or related actions in the same jurisdiction
arising out of the same general allegations or circumstances. An indemnifying
party shall not be liable for any settlement of any proceeding effected without
its written consent. However, if settled with such consent or if there be a
final judgment for the plaintiff, the indemnifying party shall indemnify the
indemnified party from and against any loss or liability by reason of such
settlement or judgment. If an indemnifying party assumes the defense of any
proceeding, it shall be entitled to settle such proceeding with the consent of
the indemnified party or, if such settlement (i) provides for an unconditional
release of the indemnified party in connection with all matters relating to the
proceeding that have been asserted against the indemnified party in such
proceeding by the other parties to such settlement and (ii) does not require an
admission of fault by the indemnified party, without the consent of the
indemnified party.

      (e) If recovery is not available under the foregoing indemnification
provisions of this Section 7 or is insufficient in respect of any liabilities
referred to therein (on grounds of public policy or otherwise), the parties
entitled to indemnification by the terms thereof shall be entitled to
contribution to liabilities and expenses, except to the extent that contribution
is not permitted under Section 11(f) of the 1933 Act. In determining the amount
of contribution to which the respective parties are entitled, there shall be
considered the relative benefits received by the Depositor on the one hand and
each Underwriter on the other from the offering of the Certificates subject to
this Agreement (taking into account the portion of the proceeds of the offering
realized by each). In the event contribution according to the foregoing sentence
is not permitted by law, in determining the amount of contribution to which the
respective parties are entitled, there shall be considered not only the relative
benefits received by the Depositor on the one hand and such Underwriter on the
other from the offering of the Certificates but also the parties' relative
knowledge and access to information concerning the matter with respect to which
the claim was asserted, the opportunity to correct and prevent any statement or
omission and any other equitable considerations appropriate under the
circumstances. The Depositor and the Underwriters agree that it would not be
equitable if the amount of such contribution were determined by pro rata or per
capita allocation (even if the Underwriters were treated as one entity for such
purpose). Notwithstanding the provisions of this subsection (e), no Underwriter
shall be required to contribute any amount in excess of the amount by which the
total underwriting discounts and commissions and other fees received by such
Underwriter in connection with the offering of the Certificates exceeds the
amount of damages that such Underwriter has otherwise been required to pay by
reason of such untrue or alleged untrue statement or omission or alleged
omission. The obligations of the Underwriters in this subsection (e) to
contribute are several in proportion to their respective underwriting
obligations and not joint.

      (f) The amount paid or payable by an indemnified party as a result of the
losses, claims, damages or other liabilities referred to in this Section 7 shall
be deemed to include any legal fees and disbursements or other expenses
reasonably incurred by such indemnified party in connection with investigating
or defending any such claim. In the event that any expenses so paid by the
indemnifying party are subsequently determined to not be required to be borne by
the indemnifying party hereunder, the party which received such payment shall
promptly refund the amount so paid to the party which made such payment. No
person guilty of fraudulent misrepresentation (within the meaning of Section
11(f) of the 1933 Act) shall be entitled to contribution from any person who was
not guilty of such fraudulent misrepresentation. The remedies provided for in
this Section 7 are not exclusive and shall not limit any rights or remedies that
may otherwise be available to any indemnified party at law or in equity.

      (g) The indemnity and contribution agreements contained in this Section 7
shall remain operative and in full force and effect regardless of (i) any
termination of this Agreement, (ii) any investigation made by the Depositor, any
Underwriter, any of their respective directors or officers, or any person
controlling the Depositor or such Underwriter, and (iii) acceptance of and
payment for any of the Certificates.

      (h) The obligations of the Depositor under this Section 7 shall be in
addition to any liability which the Depositor may otherwise have and shall
extend, upon the same terms and conditions, to each officer and director of any
Underwriter and to each person, if any, who controls any Underwriter within the
meaning of the 1933 Act or the Exchange Act; and the obligations of the
Underwriters under this Section 7 shall be in addition to any liability which
the respective Underwriters may otherwise have and shall extend, upon the same
terms and conditions, to each officer and director of the Depositor and to each
person, if any, who controls the Depositor within the meaning of the 1933 Act or
Exchange Act.

      (i) Each Underwriter will indemnify and hold harmless the other
Underwriters and each person, if any, who controls such Underwriters within the
meaning of either the 1933 Act or the Exchange Act (the "Non-Indemnifying
Underwriters") from and against any and all expenses, losses, claims, damages or
liabilities, joint or several, to which the Non-Indemnifying Underwriters
becomes subject under the 1933 Act, the Exchange Act or other federal or state
statutory law or regulation, common law or otherwise, insofar as such expenses,
losses, claims, damages or liabilities (or actions in respect thereof) arise out
of or are based upon (i) any untrue statement or alleged untrue statement of a
material fact or the omission or alleged omission (when read in conjunction with
the Rule 159 Information) to state a material fact necessary in order to make
the statements, in light of the circumstances under which they were made, not
misleading at the Time of Sale, contained in any Underwriter Free Writing
Prospectus prepared by or on behalf of, or used or referred to by, such
indemnifying Underwriter or (ii) the failure of such indemnifying Underwriter,
or any member of its selling group to comply with any provision of Section 8
hereof. In addition, each Underwriter agrees to reimburse, as incurred, such
Non-Indemnifying Underwriters for any legal or other expenses reasonably
incurred by them in connection with investigating or defending against any such
loss, claim, damage, liability or action, except to the extent that the
Non-Indemnifying Underwriters are entitled to indemnification or contribution
therefor from any Mortgage Loan Seller pursuant to any Indemnification
Agreement. This agreement will be in addition to any liability that any
Underwriter may otherwise have.

      8. Offering Communications; Free Writing Prospectuses.

      (a) Unless preceded or accompanied by a prospectus satisfying the
requirements of Section 10(a) of the 1933 Act, no Underwriter shall convey or
deliver any written communication to any person in connection with the initial
offering of the Certificates, unless such written communication (i) is made in
reliance on Rule 134 under the 1933 Act, (ii) constitutes a prospectus
satisfying the requirements of Rule 430B under the 1933 Act or (iii) constitutes
Rule 159 Information or a Free Writing Prospectus. Without limitation thereby,
without the prior written consent of the Depositor (which consent may be
withheld for any reason), no Underwriter shall prepare, convey or deliver in
connection with the initial offering of the Certificates any Free Writing
Prospectus or "ABS informational and computational material," as defined in Item
1101(a) of Regulation AB under the 1933 Act ("ABS Informational and
Computational Material"), in reliance upon Rules 167 and 426 under the 1933 Act
other than materials provided to it by Credit Suisse Securities (USA) LLC or the
Depositor.

      (b) Each Underwriter shall deliver to the Depositor, no later than two
business days prior to the date of first use thereof or such later date as may
be agreed to by the Depositor, (i) any Free Writing Prospectus that was prepared
by or on behalf of such Underwriter (an "Underwriter Free Writing Prospectus")
and that contains any "issuer information," as defined in Rule 433(h) under the
1933 Act and footnote 271 of the Commission's Securities Offering Reform Release
No. 33-8591 ("Issuer Information") (which the parties hereto agree includes,
without limitation, Mortgage Loan Seller Information), and (ii) any Free Writing
Prospectus or portion thereof prepared by or on behalf of such Underwriter that
contains only a description of the final terms of the Certificates.
Notwithstanding the foregoing, any Free Writing Prospectus that contains only
ABS Informational and Computational Materials may be delivered by an Underwriter
to the Depositor not later than the later of (A) two business days prior to the
due date for filing of the Prospectus pursuant to Rule 424(b) under the 1933 Act
or such later date as may be agreed to by the Depositor or (B) the date of first
use of such Free Writing Prospectus.

      (c) Each Underwriter represents and warrants to the Depositor that the
Free Writing Prospectuses to be furnished to the Depositor by such Underwriter
pursuant to Section 8(b) hereof will constitute all Free Writing Prospectuses of
the type described therein that were furnished to prospective investors by such
Underwriter in connection with its offer and sale of the Certificates.

      (d) Each Underwriter represents and warrants to the Depositor that each
Free Writing Prospectus required to be provided by it to the Depositor pursuant
to Section 8(b) hereof did not, as of the date such Free Writing Prospectus was
conveyed or delivered to any prospective investor, include any untrue statement
of a material fact or omit to state any material fact required to be stated
therein or necessary to make the statements contained therein (when read in
conjunction with the Rule 159 Information), in light of the circumstances under
which they were made, not misleading; provided however, that no Underwriter
makes any representation to the extent such misstatements or omissions were the
result of any inaccurate Issuer Information supplied by the Depositor or any
Mortgage Loan Seller to such Underwriter, which information was not corrected by
information subsequently supplied by the Depositor or any Mortgage Loan Seller
to such Underwriter within a reasonable period of time prior to the Time of
Sale.

      (e) The Depositor agrees to file with the Commission the following:

            (i) Any Issuer Free Writing Prospectus;

            (ii) Any Free Writing Prospectus or portion thereof delivered by an
Underwriter to the Depositor pursuant to Section 8(b) hereof; and

            (iii) Any Free Writing Prospectus for which the Depositor or any
person acting on its behalf provided, authorized or approved information that is
prepared and published or disseminated by a person unaffiliated with the
Depositor or any other offering participant that is in the business of
publishing, radio or television broadcasting or otherwise disseminating
communications.

      Notwithstanding the foregoing, the Depositor shall not be required to file
(1) Issuer Information contained in any Underwriter Free Writing Prospectus or
Free Writing Prospectus of any other offering participant other than the
Depositor, if such information is included or incorporated by reference in a
prospectus or Free Writing Prospectus previously filed with the Commission that
relates to the offering of the Certificates, or (2) any Free Writing Prospectus
or portion thereof that contains a description of the Certificates or the
offering of the Certificates which does not reflect the final terms thereof.

      (f) Any Free Writing Prospectus required to be filed pursuant to Section
8(e) hereof by the Depositor shall be filed with the Commission not later than
the date of first use of the Free Writing Prospectus, except that:

            (i) any Free Writing Prospectus or portion thereof required to be
filed that contains only the description of the final terms of the Certificates
may be filed by the Depositor within two (2) days of the later of the date such
final terms have been established for all classes of Certificates and the date
of first use;

            (ii) any Free Writing Prospectus or portion thereof required to be
filed that contains only ABS Informational and Computational Material may be
filed by the Depositor with the Commission not later than the later of the due
date for filing the final Prospectus relating to the Certificates pursuant to
Rule 424(b) under the 1933 Act or two (2) business days after the first use of
such Free Writing Prospectus;

            (iii) any Free Writing Prospectus required to be filed pursuant to
Section 8(e)(iii) hereof may, if no payment has been made or consideration has
been given by or on behalf of the Depositor for the Free Writing Prospectus or
its dissemination, be filed by the Depositor with the Commission not later than
four (4) business days after the Depositor becomes aware of the publication,
radio or television broadcast or other dissemination of the Free Writing
Prospectus; and

            (iv) the Depositor shall not be required to file (A) Issuer
Information contained in any Free Writing Prospectus of an Underwriter or any
offering participant other than the Depositor, if such information is included
or incorporated by reference in a prospectus or Free Writing Prospectus
previously filed with the Commission that relates to the offering of the
Certificates, or (B) any Free Writing Prospectus or portion thereof that
contains a description of the Certificates or the offering of the Certificates
which does not reflect the final terms thereof.

      (g) Each Underwriter shall file with the Commission, or provide to the
Depositor at least two business days prior to the time such filing is required,
any Free Writing Prospectus that is used or referred to by it and distributed by
or on behalf of such Underwriter which is neither an Issuer Free Writing
Prospectus nor contains Issuer Information in a manner reasonably designed to
lead to its broad, unrestricted dissemination not later than the date of the
first use of such Free Writing Prospectus.

      (h) Notwithstanding the provisions of Section 8(g) hereof, each
Underwriter shall file with the Commission any Free Writing Prospectus for which
such Underwriter or any person acting on its behalf provided, authorized or
approved information that is prepared and published or disseminated by a person
unaffiliated with the Depositor or any other offering participant that is in the
business of publishing, radio or television broadcasting or otherwise
disseminating written communications and for which no payment was made or
consideration given by or on behalf of the Depositor or any other offering
participant, not later than four (4) business days after the Underwriter becomes
aware of the publication, radio or television broadcast or other dissemination
of the Free Writing Prospectus.

      (i) Notwithstanding the provisions of Sections 8(e) and 8(g) hereof,
neither the Depositor nor any Underwriter shall be required to file any Free
Writing Prospectus that does not contain substantive changes from or additions
to a Free Writing Prospectus previously filed with the Commission.

      (j) The Depositor and the Underwriters each agree that any Free Writing
Prospectuses prepared by it shall contain the following legend, or substantially
equivalent legend that complies with Rule 433 of the 1933 Act:

      "We have filed a registration statement (including a prospectus) with the
Securities and Exchange Commission for the offering to which this communication
relates. Before you invest, you should read the prospectus in the registration
statement and other documents the depositor has filed with the Securities and
Exchange Commission for more complete information about us, the issuing trust
and this offering. You may get these documents for free by visiting EDGAR on the
Securities and Exchange Commission web site at www.sec.gov. Alternatively, the
depositor, any underwriter or any dealer participating in the offering will
arrange to send you the prospectus after filing if you request it by calling
toll free 1.800.221.1037 or by email to the following address:
barry.polen@csfb.com."

      (k) The Depositor and the Underwriters each agree to retain all Free
Writing Prospectuses that they have used and that are not required to be filed
pursuant to this Section 8 for a period of three (3) years following the initial
bona fide offering of the Certificates.

      (l) (i) In the event that the Depositor becomes aware that, as of the Time
of Sale, any Issuer Free Writing Prospectus contains any untrue statement of a
material fact or omits to state a material fact necessary in order to make the
statements contained therein (when read in conjunction with the Rule 159
Information), in light of the circumstances under which they were made, not
misleading (a "Defective Issuer Free Writing Prospectus"), the Depositor shall
notify the Underwriters of such untrue statement or omission within one business
day after discovery and the Depositor shall, if requested by the Underwriters,
prepare and deliver to the Underwriters a Free Writing Prospectus that corrects
the material misstatement or omission in the Defective Issuer Free Writing
Prospectus (such corrected Issuer Free Writing Prospectus, a "Corrected Issuer
Free Writing Prospectus").

            (ii) In the event that any Underwriter becomes aware that, as of the
      Time of Sale, any Underwriter Free Writing Prospectus delivered to an
      investor in any Certificates contained any untrue statement of a material
      fact or omitted to state a material fact necessary in order to make the
      statements contained therein (when read in conjunction with the Rule 159
      Information), in light of the circumstances under which they were made,
      not misleading (together with a Defective Issuer Free Writing Prospectus,
      a "Defective Free Writing Prospectus"), such Underwriter shall notify the
      Depositor of such untrue statement or omission within one business day
      after discovery.

            (iii) The Underwriters shall, if requested by the Depositor:

      (a) if the Defective Free Writing Prospectus was an Underwriter Free
Writing Prospectus, prepare a Free Writing Prospectus that corrects the material
misstatement in or omission from the Defective Free Writing Prospectus (together
with a Corrected Issuer Free Writing Prospectus, a "Corrected Free Writing
Prospectus");

      (b) deliver the Corrected Free Writing Prospectus to each investor which
received the Defective Free Writing Prospectus prior to entering into a contract
of sale with such investor;

      (c) notify such investor in a prominent fashion that the prior contract of
sale with the investor has been terminated, and of the investor's rights as a
result of termination of such agreement;

      (d) provide such investor with an opportunity to affirmatively agree to
purchase the Certificates on the terms described in the Corrected Free Writing
Prospectus; and

      (e) comply with any other requirements for reformation of the original
contract of sale with such investor, as described in Section IV.A.2.c of
Commission's Securities Offering Reform Release No. 33-8591.

            (iv) In the event that the Defective Free Writing Prospectus was an
      Issuer Free Writing Prospectus, and the Underwriters shall in good faith
      incur any costs to an investor in connection with the reformation of the
      contract of sale with the investor, the Depositor agrees to reimburse the
      Underwriters for such costs; provided that, before incurring such costs,
      the Underwriters first permits the Depositor access to the applicable
      investor and an opportunity to attempt to mitigate such costs through
      direct negotiation with such investor.

            (iv) Each Underwriter covenants with the Depositor that after the
      final Prospectus is available the Underwriter shall not distribute any
      written information concerning the Certificates to a prospective investor
      unless such information is preceded or accompanied by the final
      Prospectus..

      (m) Each Underwriter covenants with the Depositor that it will make
available to the Depositor such personnel as are familiar with the Underwriter's
compliance procedures for the purpose of answering questions concerning the
Underwriter's practices and procedures for the preparation and dissemination of
written materials concerning the Certificates to prospective investors prior to
the delivery of the final Prospectus to such investors.

      9. Default of Underwriters. If any Underwriter defaults in its obligations
to purchase Certificates hereunder and the aggregate principal amount of
Certificates that such defaulting Underwriter or Underwriters agreed but failed
to purchase does not exceed 10% of the total principal amount of Certificates to
be purchased hereunder, Credit Suisse Securities (USA) LLC may make arrangements
satisfactory to the Depositor for the purchase of such Certificates by other
persons, but if no such arrangements are made by such Closing Date, the
non-defaulting Underwriters shall be obligated to purchase the Certificates that
such defaulting Underwriter agreed but failed to purchase hereunder. If any
Underwriter so defaults and the aggregate principal amount of Certificates with
respect to which such default occurs exceeds 10% of the total principal amount
of Certificates to be purchased hereunder and arrangements satisfactory to
Credit Suisse Securities (USA) LLC and the Depositor for the purchase of such
Certificates by other persons are not made within 36 hours after such default,
this Agreement will terminate without liability on the part of any
non-defaulting Underwriter or the Depositor, except as provided in Section 10.
As used in this Agreement, the term "Underwriter" includes any person
substituted for an Underwriter under this Section. Nothing herein will relieve a
defaulting Underwriter from liability for its default.

      10. Termination of the Obligations of the Underwriters. (a) Any
Underwriter may terminate its obligations under this Agreement by notice to the
Depositor at any time at or prior to the Specified Delivery Date if the sale of
the Certificates provided for herein is not consummated because of any failure
or refusal on the part of the Depositor to comply with the terms or to fulfill
any of the conditions of this Agreement, or if for any reason the Depositor
shall be unable to perform its obligations under this Agreement.

      (b) The obligations of the Underwriters to purchase on the Specified
Delivery Date the Certificates described in Schedule I shall be terminable by
Credit Suisse Securities (USA) LLC if at any time on or prior to the Specified
Delivery Date (i) any change, or any development or event involving a
prospective change in the condition (financial or other), business, properties
or results of operations of the Depositor or the Trust which, in the judgment of
a majority in interest of the Underwriters (based on Underwriting obligations)
including Credit Suisse Securities (USA) LLC is material and adverse and makes
it impractical or inadvisable to proceed with completion of the public offering
or the sale of and payment for the Certificates; (ii) any downgrading in the
rating of any of the Certificates by any "nationally recognized statistical
rating organization" (as defined for purposes of Rule 436(g) under the 1933
Act), or any public announcement that any such organization has under
surveillance or review its rating of any of the Certificates (other than an
announcement with positive implications of a possible upgrading, and no
implication of a possible downgrading, of such rating); (iii) any change in U.S.
or international financial, political or economic conditions or currency
exchange rates or exchange controls as would, in the judgment of a majority in
interest of the Underwriters including Credit Suisse Securities (USA) LLC be
likely to prejudice materially the success of the proposed issue, sale or
distribution of the Certificates, whether in the primary market or in respect of
dealings in the secondary market; (iv) any material suspension or material
limitation of trading in securities generally on the New York Stock Exchange or
any setting of minimum prices for trading on such exchange, or any suspension of
trading of any Certificates on any relevant exchange or in the over-the-counter
market; (v) any general moratorium on commercial banking activities declared by
any Federal or New York State authorities; (vi) any major disruption of
settlements of securities or clearance services in the United States; or (vii)
any attack on, outbreak or escalation of hostilities or act of terrorism
involving the United States, any declaration of war by Congress or any other
national or international calamity or emergency if, in the judgment of a
majority in interest of the Underwriters including Credit Suisse Securities
(USA) LLC the effect of any such attack, outbreak, escalation, act, declaration,
calamity or emergency makes it impractical or inadvisable to proceed with
completion of the public offering or the sale of any payment for the
Certificates.

      (c) If any Underwriter terminates its obligations under this Agreement in
accordance with Section 10(a), the Depositor shall reimburse such Underwriter
for all reasonable out-of pocket expenses (including reasonable fees and
disbursements of counsel) that shall have been reasonably incurred by such
Underwriter in connection with the proposed purchase and sale of the
Certificates.

      11. Survival of Certain Representations and Obligations. The respective
indemnities, agreements, representations, warranties and other statements by the
Depositor and of the several Underwriters set forth in or made pursuant to this
Agreement shall remain in full force and effect, regardless of any investigation
or statement as to the results thereof made by or on behalf of such
Underwriters, the Depositor or any of their respective officers or directors or
any controlling person, and shall survive delivery of and payment of the related
Certificates.

      If this Agreement is terminated pursuant to Section 10 above or if for any
reason the purchase by the Underwriters of the Certificates described in
Schedule I is not consummated, the Depositor shall remain responsible for the
expenses to be paid or reimbursed by it pursuant to Section 5(g) above, and the
obligations of the Depositor and such Underwriters pursuant to Section 7 above
shall remain in effect.

      12. Obligations of Column Financial, Inc. Column Financial, Inc. agrees
with the Underwriters, for the sole and exclusive benefit of the Underwriters
and each of their respective officers, directors and any other person, if any,
who controls the Underwriters within the meaning of the 1933 Act or the Exchange
Act and not for the benefit of any assignee thereof or any other person or
persons dealing with the Underwriters, to indemnify and hold harmless the
Underwriters against any failure by the Depositor to perform its obligations to
the Underwriters and their officers, directors and control persons pursuant to
Section 7(a) hereof.

      13. Notices. All communications hereunder shall be in writing and, if sent
to Credit Suisse First Boston LLC, shall be mailed, delivered or telecopied to
it at Credit Suisse First Boston LLC, Eleven Madison Avenue, New York, New York
10010, Attention: Edmund Taylor, with a copy to Casey McCutcheon, Esq., Legal &
Compliance Department, Telecopy No.: (917) 326-8433; if sent to McDonald
Investments Inc., shall be mailed, delivered or telecopied to it at McDonald
Investments Inc., 127 Public Square, Cleveland, Ohio 44114, Attention: Joe
Chinnici, Telecopy No.: (216) 689-4233 (with a copy to Richard Hawrylak,
Telecopy No.: (216) 689-5681); if sent to GMAC Commercial Holding Capital
Markets Corp., shall be mailed, delivered or telecopied to it at GMAC Commercial
Holding Capital Markets Corp., 200 Witmer Road, Horsham, Pennsylvania 19044,
Attention: David M. Lazarus, Telecopy No.: (215) 328-1775; if sent to Banc of
America Securities LLC shall be mailed, delivered or telecopied to it at Banc of
America Securities LLC, 214 North Tryon Street, NC1-027-22-03, Charlotte, North
Carolina 28255, Attention: Stephen Hogue, Telecopy No.: (704) 386-1094, with a
copy to Paul Kurzeja, Esq., Legal Department, Telecopy No.: (704) 409-0267; or
if sent to the Depositor, shall be mailed, delivered or telecopied to it at
Credit Suisse First Boston Mortgage Securities Corp., Eleven Madison Avenue, New
York, New York 10010, Attention: Edmund Taylor, with a copy to Casey McCutcheon,
Esq., Legal & Compliance Department, Telecopy No.: (917) 326-8433; provided,
however, that any notice to an Underwriter pursuant to Section 7 shall be
mailed, delivered or telecopied to such Underwriter at the address furnished by
it.

      14. No Fiduciary Duty. The Depositor acknowledges and agrees that the
Underwriters are acting solely in the capacity of an arm's length contractual
counterparty to the Depositor with respect to the offering of the Certificates
contemplated hereby (including in connection with determining the terms of the
offering) and not as a financial advisor or a fiduciary to, or an agent of, the
Depositor or any other person. Additionally, neither Credit Suisse nor any other
Underwriter is advising the Depositor or any other person as to any legal, tax,
investment, accounting or regulatory matters in any jurisdiction. The Depositor
shall consult with its own advisors concerning such matters and shall be
responsible for making their own independent investigation and appraisal of the
transactions contemplated hereby, and the Underwriters shall have no
responsibility or liability to the Depositor with respect thereto. Any review by
the Underwriters of the Depositor, the transactions contemplated hereby or other
matters relating to such transactions will be performed solely for the benefit
of the Underwriters and shall not be on behalf of the Depositor.

      15. Successors. This Agreement shall inure to the benefit of and be
binding upon the parties hereto and their respective successors and the
officers, directors and controlling persons referred to in Section 7 above, and
their successors and assigns, and no other person shall have any right or
obligation hereunder. No purchaser of any Certificates from any Underwriter
shall be deemed a successor or assign by reason merely of such purchase.

      16. APPLICABLE LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

      17. Counterparts. This Agreement may be executed in any number of
counterparts, each of which shall be deemed to be an original, but all such
counterparts shall together constitute one and the same Agreement.

      If the foregoing is in accordance with your understanding of our
agreement, please sign and return to us a counterpart hereof, whereupon it will
become a binding agreement among the Depositor and the several Underwriters in
accordance with its terms. Alternatively, the execution of this Agreement by the
Depositor and its acceptance by or on behalf of the Underwriters may be
evidenced by an exchange of telegraphic or other written communications.

                                                     Very truly yours,



                     [SIGNATURES COMMENCE ON FOLLOWING PAGE]


<PAGE>






                                         CREDIT SUISSE FIRST BOSTON MORTGAGE
                                                SECURITIES CORP.,

                                                as Depositor

                                         By: ___________________________________
                                             Name:
                                             Title


The foregoing Agreement is hereby confirmed and accepted as of the date first
above written.

CREDIT SUISSE SECURITIES (USA) LLC,
     as Underwriter

By:___________________________________________
Name:
Title:

GMAC COMMERCIAL HOLDING CAPITAL MARKETS CORP.,
     as Underwriter

By:___________________________________________
Name:
Title:

                     [SIGNATURES CONTINUE ON FOLLOWING PAGE]


<PAGE>




MCDONALD INVESTMENTS INC.,
     as Underwriter

By:  _________________________________________
     Name:
     Title:

BANC OF AMERICA SECURITIES LLC,
     as Underwriter

By:___________________________________________
Name:
Title:

Acknowledged and agreed solely as to Section 12:

COLUMN FINANCIAL, INC.


By:  _________________________________________
     Name:
     Title:


<PAGE>





                                   SCHEDULE I

Prospectus: Prospectus Supplement dated March 7, 2006 and Base Prospectus dated
March 7, 2006 (Registration Statement No.: 333-129918)


Aggregate Principal Amount of Offered Certificates: $2,785,803,000 (approximate)


Aggregate Purchase Price to be Paid by Credit Suisse Securities (USA) LLC:
$2,785,803,000 plus accrued interest


Aggregate Purchase Price to be Paid by GMAC Commercial Holding Capital Markets
Corp.: $0 plus accrued interest


Aggregate Purchase Price to be Paid by Banc of America Securities LLC: $0 plus
accrued interest


Aggregate Purchase Price to be Paid by McDonald Investments Inc.: $0 plus
accrued interest



Certificate Balances/Notional Balance:

            Class A-1      $101,000,000
            Class A-2      $235,000,000
            Class A-3      $336,916,000
           Class A-AB      $155,000,000
            Class A-4      $698,000,000
           Class A-1-A     $576,577,000
            Class A-M      $300,356,000
            Class A-J      $236,531,000
            Class B         $18,772,000
            Class C         $37,545,000
            Class D         $33,790,000
            Class E         $22,526,000
            Class F         $33,790,000

Ratings (S&P/Fitch):
                  Class A-1          AAA/AAA
                  Class A-2          AAA/AAA
                  Class A-3          AAA/AAA
                  Class A-AB         AAA/AAA
                  Class A-4          AAA/AAA
                 Class A-1-A         AAA/AAA
                  Class A-M          AAA/AAA
                  Class A-J          AAA/AAA
                   Class B           AA+/AA+
                   Class C           AA/AA
                   Class D           AA-/AA-
                   Class E           A+/A+
                   Class F           A/A
Pass-Through Rates:
                  Class A-1          4.3670%
                  Class A-2          5.5120%
                  Class A-3          5.7110%
                  Class A-AB         5.6810%
                  Class A-4          5.6090%
                 Class A-1-A         5.6110%
                  Class A-M          5.7375%
                  Class A-J          5.7375%
                   Class B           5.7375%
                   Class C           5.7375%
                   Class D           5.7375%
                   Class E           5.7375%
                   Class F           5.7375%






<PAGE>





                                                Certificates Purchased

                                                 Certificate Balances
<TABLE>
<CAPTION>

                                               Class A-1           Class A-2           Class A-3           Class A-AB
                                              Certificate         Certificate         Certificate         Certificate
               Underwriter                      Balance             Balance             Balance             Balance
               -----------                      -------             -------             -------             -------
<S>                                           <C>                 <C>                 <C>                 <C>
Credit Suisse Securities (USA) LLC            $101,000,000        $235,000,000        $336,916,000        $155,000,000
GMAC Commercial Holding Capital Markets
Corp.                                              $0                  $0                  $0                  $0
McDonald Investments Inc.                          $0                  $0                  $0                  $0
Banc of America Securities LLC                     $0                  $0                  $0                  $0

         Total                                $101,000,000       $235,000,000]        $336,916,000        $155,000,000
</TABLE>



<TABLE>
<CAPTION>
                                               Class A-4          Class A-1-A          Class A-M           Class A-J
                                              Certificate         Certificate         Certificate         Certificate
               Underwriter                      Balance             Balance             Balance             Balance
               -----------                      -------             -------             -------             -------
<S>                                           <C>                 <C>                 <C>                 <C>
Credit Suisse Securities (USA) LLC            $698,000,000        $576,577,000        $300,356,000        $236,531,000
GMAC Commercial Holding Capital Markets
Corp.                                              $0                  $0                  $0                  $0
McDonald Investments Inc.                          $0                  $0                  $0                  $0
Banc of America Securities LLC                     $0                  $0                  $0                  $0

         Total                                $698,000,000        $576,577,000        $300,356,000        $236,531,000
</TABLE>



<TABLE>
<CAPTION>
                                        Class B            Class C           Class D           Class E           Class F
                                      Certificate        Certificate       Certificate       Certificate       Certificate
           Underwriter                  Balance            Balance           Balance           Balance           Balance
           -----------                  -------            -------           -------           -------           -------
<S>                                   <C>                <C>               <C>               <C>               <C>
Credit Suisse Securities (USA) LLC    $18,772,000        $37,545,000       $33,790,000       $22,526,000       $33,790,000
GMAC Commercial Holding Capital
Markets Corp.                              $0                $0                 $0               $0                $0
McDonald Investments Inc.                  $0                $0                 $0               $0                $0
Banc of America Securities LLC             $0                $0                 $0               $0                $0

         Total                        $18,772,000        $37,545,000       $33,790,000       $22,526,000       $33,790,000
</TABLE>