10-D 1 csm07003_10d-200709.txt UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington D.C. 20549 FORM 10-D ASSET-BACKED ISSUER DISTRIBUTION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the monthly distribution period from: August 28, 2007 to September 25, 2007 Commission File Number of issuing entity: 333-135481-17 CSMC Mortgage-Backed Trust 2007-3 (Exact name of issuing entity as specified in its charter) Commission File Number of depositor: 333-135481 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) New York (State or other jurisdiction of incorporation or organization of the issuing entity) 54-2199262 54-2199263 54-2199264 54-2199265 54-2199266 54-6740330 (I.R.S. Employer Identification No.) c/o Wells Fargo Bank, N.A. 9062 Old Annapolis Rd. Columbia, MD 21045 (Address of principal executive offices of the issuing entity) (Zip Code) (410) 884-2000 (Telephone number, including area code) Not Applicable (Former name, former address, if changed since last report) Registered/reporting pursuant to (check one) Title of Section Section Section Name of Exchange Class 12(b) 12(g) 15(d) (If Section 12(b)) 1-A-1-A _____ _____ __X___ ____________ 1-A-1-B _____ _____ __X___ ____________ 1-A-2 _____ _____ __X___ ____________ 1-A-3-A _____ _____ __X___ ____________ 1-A-3-B _____ _____ __X___ ____________ 1-A-4 _____ _____ __X___ ____________ 1-A-5 _____ _____ __X___ ____________ 1-A-6-A _____ _____ __X___ ____________ 1-A-6-B _____ _____ __X___ ____________ 1-M-1 _____ _____ __X___ ____________ 1-M-2 _____ _____ __X___ ____________ 1-M-3 _____ _____ __X___ ____________ 1-M-4 _____ _____ __X___ ____________ 1-M-5 _____ _____ __X___ ____________ 1-B-1 _____ _____ __X___ ____________ 1-X _____ _____ __X___ ____________ 1-P _____ _____ __X___ ____________ 1-R _____ _____ __X___ ____________ 2-A-1 _____ _____ __X___ ____________ 2-A-2 _____ _____ __X___ ____________ 2-A-3 _____ _____ __X___ ____________ 2-A-4 _____ _____ __X___ ____________ 2-A-5 _____ _____ __X___ ____________ 2-A-6 _____ _____ __X___ ____________ 2-A-7 _____ _____ __X___ ____________ 2-A-8 _____ _____ __X___ ____________ 2-A-9 _____ _____ __X___ ____________ 2-A-10 _____ _____ __X___ ____________ 2-A-11 _____ _____ __X___ ____________ 2-A-12 _____ _____ __X___ ____________ 2-A-13 _____ _____ __X___ ____________ 2-A-14 _____ _____ __X___ ____________ 2-A-15 _____ _____ __X___ ____________ 2-A-16 _____ _____ __X___ ____________ 2-A-17 _____ _____ __X___ ____________ 2-A-18 _____ _____ __X___ ____________ 2-A-19 _____ _____ __X___ ____________ 3-A-1 _____ _____ __X___ ____________ 3-A-2 _____ _____ __X___ ____________ 3-A-3 _____ _____ __X___ ____________ 3-A-4 _____ _____ __X___ ____________ 4-A-1 _____ _____ __X___ ____________ 4-A-2 _____ _____ __X___ ____________ 4-A-3 _____ _____ __X___ ____________ 4-A-4 _____ _____ __X___ ____________ 4-A-5 _____ _____ __X___ ____________ 4-A-6 _____ _____ __X___ ____________ 4-A-7 _____ _____ __X___ ____________ 4-A-8 _____ _____ __X___ ____________ 4-A-9 _____ _____ __X___ ____________ 4-A-10 _____ _____ __X___ ____________ 4-A-11 _____ _____ __X___ ____________ 4-A-12 _____ _____ __X___ ____________ 4-A-13 _____ _____ __X___ ____________ 4-A-14 _____ _____ __X___ ____________ 4-A-15 _____ _____ __X___ ____________ C-B-1 _____ _____ __X___ ____________ C-B-2 _____ _____ __X___ ____________ C-B-3 _____ _____ __X___ ____________ C-B-4 _____ _____ __X___ ____________ C-B-5 _____ _____ __X___ ____________ C-B-6 _____ _____ __X___ ____________ AP _____ _____ __X___ ____________ A-X _____ _____ __X___ ____________ PP _____ _____ __X___ ____________ AR _____ _____ __X___ ____________ AR-L _____ _____ __X___ ____________

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes __X__ No ____ Part I - DISTRIBUTION INFORMATION Item 1. Distribution and Pool Performance Information On September 25, 2007 a distribution was made to holders of CSMC Mortgage-Backed Trust 2007-3. The distribution report is attached as an Exhibit to this Form 10-D. Please see Item 9(b), Exhibit 99.1 for the related information. Part II - OTHER INFORMATION Item 9. Exhibits. (a) The following is a list of documents filed as part of this Report on Form 10-D: (99.1) Monthly report distributed to holders of CSMC Mortgage-Backed Trust 2007-3, relating to the September 25, 2007 distribution. (b) The exhibits required to be filed by the Registrant pursuant to this Form are listed above and in the Exhibit Index that immediately follows the signature page hereof. SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized. Credit Suisse First Boston Mortgage Securities Corp. (Depositor) /s/ Kevin Steele Kevin Steele, Vice President Date: October 02, 2007 EXHIBIT INDEX Exhibit Number Description EX-99.1 Monthly report distributed to holders of CSMC Mortgage-Backed Trust 2007-3, relating to the September 25, 2007 distribution. EX-99.1 Credit Suisse First Boston Mortgage Securities Corp. Mortgage-Backed P/T Certificates Distribution Date: 9/25/2007 Credit Suisse First Boston Mortgage Securities Corp. Mortgage-Backed P/T Certificates Series 2007-3 Contact: Customer Service - CTSLink Wells Fargo Bank, N.A. Securities Administration Services 8480 Stagecoach Circle Frederick, MD 21701-4747 www.ctslink.com Telephone: 1-866-846-4526 Fax: 240-586-8675

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CSMC Mortgage-Backed Trust 2007-3 10-D