**UNITED
        STATES**
 **SECURITIES
        AND EXCHANGE COMMISSION**
 **Washington,
        DC 20549**
  
 **FORM
        10-K**
 
 (Mark
        One)
  [X]
              ANNUAL
                  REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
                  ACT OF
                  1934
  For
        the
        fiscal year ended December
        31,
        2006
  OR
  [  ]
              TRANSITION
                  REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
                  ACT OF
                  1934
  For
        the
        transition period from  to
  Commission
        file number  333-130333-06
 
  Citicorp
                  Mortgage Securities Trust, Series 2006-4(Exact
                  name of issuing entity as specified in its
                  charter)
 
  Citicorp
                  Mortgage Securities, Inc.(Exact
                  name of depositor as specified in its
                  charter)
 
  CitiMortgage,
                  Inc.(Exact
                  name of sponsor as specified in its
                  charter)
 
  New
                  York
              
              13-4341340,
                  13-4341345 and 13-4341349(State
                  or Other Jurisdiction of Incorporation or Organization of Issuing
                  Entity)
              
              (I.R.S.
                  Employer Identification Number of
                Issuing
                  Entity)1000
                  Technology Drive, O’Fallon, Missouri
              
              63368-2240(Address
                  of Principal Executive
                Offices
                  of Issuing Entity)
              
              (Zip
                  Code)
 
 Registrant’s
        telephone number, including area code (636)
        261-1313
 
 Securities
        Registered pursuant to Section 12(b) of the Exchange
        Act:       NONE
 
 Securities
        Registered pursuant to Section 12(g) of the
        Act:       NONE
 
 Indicate
        by check mark if the registrant is a well-known seasoned issuer, as defined
        in
        Rule 405 of the Securities Act.  [  ]
        Yes   [X] No
 
 Indicate
        by check mark if the registrant is not required to file reports pursuant
        to
        Section 13 or Section 15(d) of the Act.  [  ]
        Yes   [X] No
 
 1
  
  
 Indicate
        by check mark whether the registrant: (1) has filed all reports required
        to be
        filed by Section 13 or 15(d) of the Exchange Act during the preceding 12 months
        (or 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.        [X] Yes [  ]
        No
 
 
 Indicate
        by check mark if disclosure of delinquent filers pursuant to Item 405 of
        Regulation S-K is not contained herein, and will not be contained, to the
        best
        of registrant’s knowledge, in definitive proxy or information statements
        incorporated by reference in Part III of this Form 10-K or any amendment
        to this
        Form 10-K.      [  ] [Item 405 of
        Regulation S-K is not applicable.]
 
 Indicate
        by check mark whether the registrant is a large accelerated filer, an
        accelerated filer, or a non-accelerated filer. See definition of “accelerated
        filer and large accelerated filer in Rule 12b-2 of the Exchange Act. (Check
        one):
 
 Large
                  Accelerated Filer [   ]
              Accelerated
                  Filer [   ]
              Non-Accelerated
                  Filer [X]
 
 Indicate
        by check mark whether the registrant is a shell company (as defined in Rule
        12b-2 of the Exchange Act).   [   ]
        Yes   [X] No
 
 State
        the
        aggregate market value of the voting and non-voting common equity held by
        non-affiliates computed by reference to the price at which the common equity
        was
        last sold, or the average bid and asked price of such common equity, as of
        the
        last business day of the registrant’s most recently completed second fiscal
        quarter.  [Not applicable.]
 
 
 **PART
        I**
  **The
        following items have been omitted pursuant to General Instruction J. to Form
        10-K:**
 
 Item
        1.          Business
 Item
        1A.       Risk Factors
 Item
        2.          Properties
 Item
        3.          Legal
        Proceedings
 Item
        4.          Submission of
        Matters to a Vote of Security Holders
 
 
 **Item
        1B.       Unresolved Staff
        Comments**
 
 None.
  
 **The
        following substitute information is provided in accordance with General
        Instruction J. to Form 10-K:**
  **Item
        1112(b) of Regulation AB**  **(Significant
        obligors of pool assets)**
  No
        single
        obligor represents more than 10% of the pool assets held by the issuing
        entity.
  **Item
        1114(b)(2) of Regulation AB**  **(Credit
        enhancement and other support, except for certain derivative instruments)
        (Information regarding significant enhancement providers)**
  No
        entity
        or group of affiliated entities provides any external credit enhancement
        for the
        certificates issued by the issuing entity.
  **Item
        1115(b) of Regulation AB**  **(Certain
        derivative instruments)**
  No
        entity
        or group of affiliated entities provides derivative instruments having a
        significance percentage of 10% or more.
 
 
 2
  
  
 **Item
        1117 of Regulation AB (Legal Proceedings)**
 
 There
        are
        no legal proceedings that would be material to investors against the sponsor,
        the depositor, the issuing entity, Citibank, N.A. (the paying agent,
        authenticating agent and certificate registrar for the issuing entity), or
        to
        CitiMortgage, Inc.’s knowledge, the trustee, nor does CitiMortgage, Inc. know of
        any such proceeding contemplated by any governmental authorities.
 
 
 **PART
        II**
 
 
 **The
        following items have been omitted pursuant to General Instruction J. of Form
        10-K:**
 
 Item
        5.        Market for Registrant’s Common
        Equity and Related Stockholder Matters and Issuer Purchases of Equity
        Securities
 Item
        6.        Selected Financial
        Data
 Item
        7.        Management’s Discussion and
        Analysis of Financial Condition and Results of Operations
 Item
        7A.     Quantitative and Qualitative Disclosures About
        Market Risk
 Item
        8.        Financial Statements and
        Supplementary Data
 Item
        9.        Changes in Disagreements With
        Accountants on Accounting and Financial Disclosure
 Item
        9A.     Controls and Procedures
  **Item
          9A(T).    Controls and Procedures**
 
 Not
          applicable.
 
 **Item
        9B.    Other Information**
 
 None.
   **PART
        III**
  
 **The
        following items have been omitted pursuant to General Instruction J. of Form
        10-K:**
  Item
        10.       Directors, Executive Officers and
        Corporate Governance
 Item
        11.       Executive Compensation
 Item
        12.       Security Ownership of Certain
        Beneficial Owners and Management and Related Stockholder Matters
 Item
        13.       Certain Relationships and Related
        Transactions, and Director Independence
 Item
        14.       Principal Accountant Fees and
        Services
 
 **The
        following substitute information is provided in accordance with General
        Instruction J. to Form 10-K:**
  **Item
        1119 of Regulation AB**  **(Affiliations
        and certain relationships and related transactions)**
  Omitted
        pursuant to the Instruction to Item 1119 of Regulation AB.
  **Item
        1122 of Regulation AB**  **(Compliance
        with applicable servicing criteria)**
  The
        reports required by Item 1122(a) and (b) of, or relating to, all parties
        determined by the registrant to be participating in the servicing function
        with
        respect to the issuing entity are attached to this Form 10-K as Exhibits
        33.1.1,
        33.1.2, 34.1.1 and 34.1.2. None of such reports identifies any instance of
        material noncompliance with the servicing criteria applicable to those
        parties.
  **Item
        1123 of Regulation AB (Servicer compliance statement)**
 
 The
        statement required by Item 1123 is attached to this Form 10-K as Exhibit
        35.1.
 
 3
  
  
 **PART
        IV**
  
 **Item
                  15.**
              **Exhibits
                  and Financial Statements and Schedules**(a)(1)
              Not
                  applicable.(a)(2)
              Not
                  applicable.(a)(3)
              Exhibits**Exhibit
                  Number**
              **Description**4.1
              Pooling
                  and Servicing Agreement, dated as ofAugust
                  1, 2006,
                  incorporated by reference from Exhibit 4.1of
                  the Issuing Entity’s Current Report onForm
                  8-K filed with the Commission on September 5, 2006.10.1
              Form
                  of Mortgage Loan Purchase Agreement, datedAugust
                  1, 2006,
                  incorporated by reference from Exhibit 10.1 of the Issuing Entity’s
                  Current Report onForm
                  8-K filed with the Commission on September 5, 2006.31.1
              Certification
                  pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 and relevant
                  rules and regulations of the Commission, dated March 28,
                  2007.33.1.1
              Management
                  Assessment of Compliance with Applicable Servicing Criteria, dated
                  February 27, 2007, of CitiMortgage, Inc.33.1.2
              Management’s
                  Assertion of Compliance, dated February 28, 2007, of Citibank,
                  N.A.34.1.1
              Report
                  of Independent Registered Public Accounting Firm, dated February
                  27, 2007,
                  of KPMG LLP, relating to Exhibit 33.1.1.34.1.2
              Report
                  of Independent Registered Public Accounting Firm, dated February
                  28, 2007,
                  of KPMG LLP, relating to Exhibit 33.1.2.35.1
              Servicer
                  Compliance Statement of CitiMortgage, Inc., dated February 27,
                  2007.
 
  4
   
  **SIGNATURES**
  
  Pursuant
        to the requirements of Section 13 or 15(d) 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.
  **Citicorp
        Mortgage Securities Trust, Series 2006-4**
  By: **CitiMortgage,
        Inc.** ,
        as
        Servicer
  By: /s/
        Herb
        Gover
 Herb
        Gover
 Executive
        Vice President, North American Consumer Asset Operations
  March
        28,
        2007
 
 
 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  5
   
  **INDEX
        TO EXHIBITS**
  
 
 **Exhibit
                  Number**
              **Description**4.1
              Pooling
                  and Servicing Agreement, dated as ofAugust
                  1, 2006,
                  incorporated by reference from Exhibit 4.1of
                  the Issuing Entity’s Current Report onForm
                  8-K filed with the Commission on September 5, 2006.10.1
              Form
                  of Mortgage Loan Purchase Agreement, datedAugust
                  1, 2006,
                  incorporated by reference from Exhibit 10.1 of the Issuing Entity’s
                  Current Report onForm
                  8-K filed with the Commission on September 5, 2006.31.1
              Certification
                  pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 and relevant
                  rules and regulations of the Commission, dated March 28,
                  2007.33.1.1
              Management
                  Assessment of Compliance with Applicable Servicing Criteria, dated
                  February 27, 2007, of CitiMortgage, Inc.33.1.2
              Management’s
                  Assertion of Compliance, dated February 28, 2007, of Citibank,
                  N.A.34.1.1
              Report
                  of Independent Registered Public Accounting Firm, dated February
                  27, 2007,
                  of KPMG LLP, relating to Exhibit 33.1.1.34.1.2
              Report
                  of Independent Registered Public Accounting Firm, dated February
                  28, 2007,
                  of KPMG LLP, relating to Exhibit 33.1.2.35.1
              Servicer
                  Compliance Statement of CitiMortgage, Inc., dated February 27,
                  2007.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 6