UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT PURSUANT

TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported)

May 30, 2007

CSMC Mortgage-Backed Trust Series 2007-4

(Issuing Entity)

Credit Suisse First Boston Mortgage Securities Corp.

(Exact Name of Depositor as Specified in its Charter)

DLJ Mortgage Capital, Inc.

(Exact Name of Sponsor as Specified in its Charter)

Credit Suisse First Boston Mortgage Securities Corp.

(Exact Name of Registrant as Specified in its Charter)

Delaware

333-140945

13-3320910

(State or Other Jurisdiction

Of Incorporation)

(Commission

File Number)

(I.R.S. Employer

Identification No.)

11 Madison Avenue

New York, NY

10010

(Address of Principal Executive Offices)

(Zip Code)

Registrant’s telephone number, including area code: (212) 325-2000

No Change

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

[ ] Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

[ ] Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

[ ] Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

[ ] Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 8.01. Other Events

Item 8.01. Other Events.

McKee Nelson LLP has been retained by this Registrant as counsel for its Registration Statement on Form S-3 (Commission File No. 333-140945) in connection with various transactions. Legal opinions by McKee Nelson LLP to be incorporated into the Registration Statement are attached hereto as Exhibit 5.1, Exhibit 8.1 and Exhibit 23.1.

Item 9.01. Financial Statements and Exhibits.

(a)

Not applicable.

(b)

Not applicable.

(c)

Not applicable.

(d)

Exhibits:

5.1

Opinion of McKee Nelson LLP as to legality (including consent of such firm).

8.1

Opinion of McKee Nelson LLP as to certain tax matters (including consent of such firm included in Exhibit 5.1).

23.1 Consent of McKee Nelson LLP (included in Exhibit 5.1).

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

CREDIT SUISSE FIRST BOSTON MORTGAGE SECURITIES CORP.

By: /s/ Kevin Steele

Name: Kevin Steele

Title: Vice President

Dated: May 30, 2007

EXHIBIT INDEX

Exhibit No.

Description

Page No.

5.1

Opinion of McKee Nelson LLP as to legality (including consent of such firm).

8.1

Opinion of McKee Nelson LLP as to certain tax matters (including consent of such firm included in Exhibit 5.1).

23.1

Consent of McKee Nelson LLP (included in Exhibit 5.1).

CSMC Trust 2007-4 8-K