UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 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 Transition period ______________________________


             Commission File Number of issuing entity: 333-126745-07
                           RFMSI SERIES 2006-S1 TRUST
           (Exact name of issuing entity as specified in its charter)

                 RESIDENTIAL FUNDING MORTGAGE SECURITIES I, INC.
              (Exact name of depositor as specified in its charter)

                        RESIDENTIAL FUNDING COMPANY, LLC
               (Exact name of sponsor as specified in its charter)

                                    New York
      (State or other jurisdiction of incorporation or organization of the
                                 issuing entity)

            c/o Residential Funding Company, LLC, as Master Servicer
                         8400 Normandale Lake Boulevard
                          Minneapolis, Minnesota 55437
 -----------------------------------------------------------------------------

           (Address of principal executive offices of issuing entity)

             (952) 857-7000 (Telephone number, including area code)

                                      None
                      (I.R.S. Employer Identification No.)

                                       N/A
           (Former name, former address, if changed since last report)

Securities  registered  pursuant to Section  12(b) of the 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 |_|  No  |X|


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  |_|

<PAGE>

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.
|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 II of the Form 10-K or any  amendment to this
Form 10-K. |X| [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 Act). Yes |_| No |X| Registrant has no voting or non-voting  common
equity outstanding held by non-affiliates.


<PAGE>


                                     PART I

THE FOLLOWING ITEMS HAVE BEEN OMITTED IN ACCORDANCE  WITH 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.

Not Applicable.

SUBSTITUTE INFORMATION PROVIDED IN ACCORDANCE WITH GENERAL INSTRUCTION J TO FORM
10-K:

ITEM 1112(B) OF REGULATION AB. SIGNIFICANT OBLIGORS OF POOL ASSETS
(FINANCIAL INFORMATION).

None.

ITEM 1114(B)(2) OF REGULATION AB: CREDIT ENHANCEMENT AND OTHER SUPPORT,
EXCEPT FOR CERTAIN DERIVATIVES INSTRUMENTS (FINANCIAL INFORMATION).

None.

ITEM 1115(B) OF REGULATION AB: CERTAIN DERIVATIVES INSTRUMENTS (FINANCIAL
INFORMATION).

Based  on the  standards  set  forth  in  Item  1115(b)  of  Regulation  AB,  no
information is required in response to this Item.

ITEM 1117 OF REGULATION AB: LEGAL PROCEEDINGS.

There are no material pending legal or other proceedings  involving the mortgage
loans or Residential Funding Company,  LLC ("Residential  Funding"),  as sponsor
and master  servicer,  Residential  Funding  Mortgage  Securities  I,  Inc.,  as
depositor,  RFMSI  Series  2006-S1  Trust,  as the issuing  entity,  Homecomings
Financial,   LLC   ("Homecomings")   and  GMAC  Mortgage,   LLC  ("GMACM"),   as
subservicers,  or other  parties  described in Item 1117 of  Regulation AB that,
individually  or in the  aggregate,  would  have a  material  adverse  impact on
investors in the securities (the "Securities") to which this report relates.

<PAGE>

Residential  Funding,  Homecomings  and GMACM are  currently  parties to various
legal  proceedings  arising  from time to time in the  ordinary  course of their
businesses,  some of which  purport to be class  actions.  Based on  information
currently available,  it is the opinion of Residential Funding,  Homecomings and
GMACM that the  eventual  outcome of any  currently  pending  legal  proceeding,
individually  or in the  aggregate,  will not have a material  adverse effect on
their ability to perform their obligations in relation to the mortgage loans. No
assurance,  however,  can be  given  that  the  final  outcome  of  these  legal
proceedings, if unfavorable,  either individually or in the aggregate, would not
have a material adverse impact on Residential Funding, Homecomings or GMACM. Any
such  unfavorable  outcome  could  adversely  affect the ability of  Residential
Funding,  Homecomings  or GMACM to perform its servicing  duties with respect to
the  mortgage  loans and  potentially  lead to the  replacement  of  Residential
Funding, Homecomings or GMACM with a successor servicer.


                                     PART II

THE FOLLOWING ITEMS HAVE BEEN OMITTED IN ACCORDANCE  WITH GENERAL  INSTRUCTION J
TO FORM 10-K:

Item 5:  Market for Registrant's Common Equity, 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 and Disagreements with Accountants on Accounting and
         Financial Disclosure.
Item 9A: Controls and Procedures.

ITEM 9B: OTHER INFORMATION.

None.

                                    PART III

THE FOLLOWING ITEMS HAVE BEEN OMITTED IN ACCORDANCE  WITH GENERAL  INSTRUCTION J
TO FORM 10-K:

Item 10: Directors and Executive Officers of the Registrant.
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.
Item 14: Principal Accountant Fees and Services.


<PAGE>

SUBSTITUTE INFORMATION PROVIDED IN ACCORDANCE WITH GENERAL INSTRUCTION J TO FORM
10-K:

ITEM 1119 OF REGULATION AB:  AFFILIATIONS AND CERTAIN RELATIONSHIPS AND
RELATED TRANSACTIONS.

Information  contemplated  by Item 1119 of  Regulation  AB has been omitted from
this report in reliance on the Instruction to Item 1119.

ITEM 1122 OF REGULATION AB: COMPLIANCE WITH APPLICABLE SERVICING CRITERIA.

Each of Residential  Funding  Company,  LLC,  Homecomings  Financial,  LLC, HSBC
Mortgage Corporation (USA), First American Real Estate Solutions of Texas, L.P.,
Wells Fargo Home  Mortgage,  Inc.,  Regulus  Group LLC,  ZC  Sterling  Insurance
Agency,  Inc.,  U.S. Bank National  Association  and Wells Fargo Bank,  National
Association  (each,  a  "Servicing  Participant")  has  been  identified  by the
registrant as a party  participating  in the servicing  function with respect to
the pool assets held by the  Issuing  Entity.  Each  Servicing  Participant  has
completed a report on an assessment of  compliance  with the servicing  criteria
applicable to such Servicing  Participant (each, a "Report on Assessment") as of
December 31, 2006 and for the period covered by this Form 10-K, which Reports on
Assessment  are  attached  as  exhibits  to this Form 10-K.  In  addition,  each
Servicing  Participant has provided an attestation report (each, an "Attestation
Report") by a  registered  independent  public  accounting  firm  regarding  its
related Report on Assessment.  Each Attestation Report is attached as an exhibit
to this Form 10-K.

A Servicing  Participant may engage one or more vendors to perform  specific and
limited,  or scripted  activities  that  address all or a portion of one or more
servicing criteria applicable to such Servicing Participant. In general in these
cases,  the Servicing  Participant  has  instituted  policies and  procedures to
monitor whether such vendors'  activities  comply in all material  respects with
such  servicing  criteria,  and may elect to take  responsibility  for assessing
compliance with the servicing criteria applicable to such vendors' activities in
such  Servicing   Participant's  Report  on  Assessment.   Where  the  Servicing
Participant  has not  instituted  such  policies  and  procedures,  or where the
Servicing  Participant  does  not  otherwise  elect to take  responsibility  for
assessing its vendors'  activities,  the vendor is itself treated as a Servicing
Participant  and is required to provide its own Report on Assessment and related
Attestation Report.

Except as disclosed below, no Report on Assessment or related Attestation Report
has identified  (i) any material  instance of  noncompliance  with the servicing
criteria  identified  in such Report on  Assessment as applicable to the related
Servicing  Participant  or  (ii)  any  material  deficiency  in  such  Servicing
Participant's policies and procedures to monitor vendor compliance.

Exceptions:

Residential  Funding  Company,   LLC:  The  Report  on  Assessment  prepared  by
Residential  Funding  Company,  LLC  and the  related  Attestation  Report  have
identified material noncompliance with one servicing criterion applicable to it.
Specifically,   with  regard  to  servicing  criterion  1122(d)(3)(i)(B)  (which
contemplates  that  reports  to  investors  provide  information  calculated  in
accordance with the terms specified in the transaction agreements),  information
required  by the  transaction  agreements  was  excluded  from,  or  incorrectly
reported in, certain of the investor  reports.  The registrant  does not believe
these  reporting  errors had any material  impacts or effects on  investors  and
corrective action was completed to address ongoing compliance.

<PAGE>

First  American Real Estate  Solutions of Texas,  L.P.: The Report on Assessment
prepared  by First  American  Real  Estate  Solutions  of  Texas,  L.P.  ("First
American") and the related Attestation Report have identified material instances
of noncompliance with one servicing  criterion  applicable to it.  Specifically,
with regard to servicing criterion  1122(d)(2)(vii)(B),  which contemplates that
reconciliations are prepared on a monthly basis for all asset-backed  securities
related bank  accounts,  First  American  did not prepare  such  reconciliations
within 30  calendar  days after the bank  statement  cut-off  date or such other
number of days specified in the related transaction agreements.

Wells Fargo Bank,  N.A.: The Report on Assessment  prepared by Wells Fargo Bank,
N.A.  ("WFB")  and the  related  Attestation  Report  have  identified  material
instances  of  noncompliance  with  two  servicing  criteria  applicable  to it.
Specifically -

   o  With regard to servicing criterion 1122(d)(3)(i),  which contemplates that
      reports to investors are  maintained in  accordance  with the  transaction
      agreements  and  applicable  SEC  requirements,  WFB  determined  that  it
      provided  incomplete  data to some  third  parties  who use  such  data to
      calculate  delinquency  ratios  and  determine  the  status of loans  with
      respect to bankruptcy,  foreclosure  or real estate owned.  Instead of the
      actual due date being provided for use in calculating  delinquencies,  the
      date of the first payment due to the security was provided.

   o  With regard to servicing  criterion  1122(d)(4)(vii),  which  contemplates
      that loss  mitigation or recovery  actions are  implemented  in accordance
      with the  requirements  established  by the  transaction  agreements,  WFB
      determined  that it did not provide  investors with prior  notification of
      intent to foreclose.

WFB indicates in Exhibit B to its Report on Assessment  that  corrective  action
was taken to address ongoing compliance.  We have not independently verified the
accuracy of WFB's assertions or the adequacy of its remediation efforts.

ITEM 1123 OF REGULATION AB: SERVICER COMPLIANCE STATEMENT.

Each of  Residential  Funding  Company,  LLC, GMAC  Mortgage,  LLC,  Homecomings
Financial, LLC and HSBC Mortgage Corporation (USA) (each, a "Servicer") has been
identified by the  registrant as a servicer with respect to the pool assets held
by the Issuing Entity. Each Servicer has provided a statement of compliance with
its  obligations  under the servicing  agreement  applicable to such Servicer (a
"Compliance  Statement")  for the period covered by this Form 10-K, in each case
signed  by an  authorized  officer  of the  related  servicer.  Each  Compliance
Statement  is attached as an exhibit to this Form 10-K.  None of the  Compliance
Statements has identified any instance where the related  Servicer has failed to
fulfill its obligations under the applicable servicing agreement in any material
respects.


                                     PART IV

ITEM 15.    EXHIBITS, FINANCIAL STATEMENT SCHEDULES.

      (a)(1) Not Applicable.

      (a)(2) Not Applicable.

      (a)(3) Not Applicable.

      (b) Exhibits.

<PAGE>


EXHIBIT
NUMBER                                  DESCRIPTION
----------   ------------------------------------------------------------------
3.1          Certificate of Incorporation of Residential Funding Mortgage
             Securities I, Inc..
3.2          Bylaws of Residential Funding Mortgage Securities I, Inc.
10.1         Series Supplement, dated as of January 1, 2006, and the Standard
             Terms of Pooling and  Servicing  Agreement,  dated as of January 1,
             2006, among  Residential  Funding  Mortgage  Securities I, Inc., as
             company,  Residential  Funding Company,  LLC (formerly  Residential
             Funding  Corporation),  as master servicer,  and U.S. Bank National
             Association, as trustee (incorporated by reference to the Report on
             Form 8-K  filed by the  Issuing  Entity  with  the  Securities  and
             Exchange Commission on February 14, 2006).
10.2         Assignment and Assumption  Agreement,  dated as of January 30, 2006
             between  Residential  Funding  Company,  LLC (formerly  Residential
             Funding Corporation) and Residential Funding Mortgage Securities I,
             Inc.  (incorporated by reference to the Report on Form 8-K filed by
             the Issuing Entity with the  Securities and Exchange  Commission on
             February 14, 2006).
31.1         Certification of Residential Funding Company,  LLC pursuant to Rule
             13a-14(d)/15d-14(d) under the Securities Exchange Act of 1934.
33.1         Report on  Assessment  of  Compliance  with  Servicing  Criteria of
             Residential  Funding  Company,  LLC as of December 31, 2006 and for
             the period covered by this Form 10-K.
33.2         Report on  Assessment  of  Compliance  with  Servicing  Criteria of
             Homecoming  Financial,  LLC as of  December  31,  2006  and for the
             period covered by this Form 10-K.
33.3.1       Report on Assessment of Compliance with Servicing  Criteria of HSBC
             Mortgage  Corporation  (USA) as of  December  31,  2006 and for the
             period covered by this Form 10-K.
33.3.2       Report on Assessment of Compliance with Servicing Criteria of First
             American  Real Estate  Solutions of Texas,  L.P. as of December 31,
             2006 and for the period covered by this Form 10-K.
33.4.1       Report on Assessment of Compliance with Servicing Criteria of
             Wells Fargo Home Mortgage, Inc. as of December 31, 2006 and for
             the period covered by this Form 10-K.
33.4.2       Report on  Assessment  of  Compliance  with  Servicing  Criteria of
             Regulus  Group  LLC as of  December  31,  2006  and for the  period
             covered by this Form 10-K.
33.4.3       Report on Assessment of Compliance with Servicing Criteria of ZC
             Sterling Insurance Agency, Inc. as of December 31, 2006 and for
             the period covered by this Form 10-K.
33.5         Report on Assessment of Compliance with Servicing  Criteria of U.S.
             Bank  National  Association  as of  December  31,  2006 and for the
             period covered by this Form 10-K.
33.6         Report on Assessment of Compliance with Servicing Criteria of Wells
             Fargo Bank,  National  Association  as of December 31, 2006 and for
             the period covered by this Form 10-K.
34.1         Attestation Report of  PricewaterhouseCoopers  LLP on Assessment of
             Compliance with Servicing Criteria relating to Residential  Funding
             Company, LLC.
34.2         Attestation Report of  PricewaterhouseCoopers  LLP on Assessment of
             Compliance   with  Servicing   Criteria   relating  to  Homecomings
             Financial, LLC.
34.3.1       Attestation  Report of KPMG LLP on Assessment  of  Compliance  with
             Servicing Criteria relating to HSBC Mortgage Corporation (USA).
34.3.2       Attestation Report of PricewaterhouseCoopers LLP on Assessment
             of Compliance with Servicing Criteria relating to First American
             Real Estate Solutions of Texas, L.P.
34.4.1       Attestation Report of KPMG LLP on Assessment of Compliance with
             Servicing Criteria relating to Wells Fargo Home Mortgage, Inc.
34.4.2       Attestation  Report of KPMG LLP on Assessment  of  Compliance  with
             Servicing Criteria relating to Regulus Group LLC.
34.4.3       Attestation Report of Ernst & Young LLP on Assessment of Compliance
             with Servicing  Criteria relating to ZC Sterling  Insurance Agency,
             Inc..
34.5         Attestation Report of Ernst & Young LLP on Assessment of
             Compliance with Servicing Criteria relating to U.S. Bank
             National Association.
34.6         Attestation Report of KPMG LLP on Assessment of Compliance with
             Servicing Criteria relating to Wells Fargo Bank, National
             Association.
35.1         Servicer Compliance Statement of Residential Funding Company,
             LLC.
35.2         Servicer Compliance Statement of GMAC Mortgage, LLC.
35.3         Servicer Compliance Statement of Homecomings Financial, LLC.
35.4         Servicer Compliance Statement of HSBC Mortgage Corporation (USA).

       (c) Not Applicable.



<PAGE>



                                   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.

Date:  March 26, 2007
                                        RFMSI SERIES 2006-S1 TRUST

                                        By:  Residential Funding Company,
                                            LLC,
                                              as Master Servicer

                                              By:  /s/ Anthony N.  Renzi
                                                  Name: Anthony N. Renzi
                                                  Title: Managing Director





<PAGE>


                                INDEX TO EXHIBITS
EXHIBIT
NUMBER                                  DESCRIPTION
----------   ------------------------------------------------------------------
3.1          Certificate of Incorporation of Residential Funding Mortgage
             Securities I, Inc..
3.2          Bylaws of Residential Funding Mortgage Securities I, Inc.
10.1         Series Supplement, dated as of January 1, 2006, and the Standard
             Terms of Pooling and  Servicing  Agreement,  dated as of January 1,
             2006, among  Residential  Funding  Mortgage  Securities I, Inc., as
             company,  Residential  Funding Company,  LLC (formerly  Residential
             Funding  Corporation),  as master servicer,  and U.S. Bank National
             Association, as trustee (incorporated by reference to the Report on
             Form 8-K  filed by the  Issuing  Entity  with  the  Securities  and
             Exchange Commission on February 14, 2006).
10.2         Assignment and Assumption  Agreement,  dated as of January 30, 2006
             between  Residential  Funding  Company,  LLC (formerly  Residential
             Funding Corporation) and Residential Funding Mortgage Securities I,
             Inc.  (incorporated by reference to the Report on Form 8-K filed by
             the Issuing Entity with the  Securities and Exchange  Commission on
             February 14, 2006).
31.1         Certification of Residential Funding Company,  LLC pursuant to Rule
             13a-14(d)/15d-14(d) under the Securities Exchange Act of 1934.
33.1         Report on  Assessment  of  Compliance  with  Servicing  Criteria of
             Residential  Funding  Company,  LLC as of December 31, 2006 and for
             the period covered by this Form 10-K.
33.2         Report on  Assessment  of  Compliance  with  Servicing  Criteria of
             Homecoming  Financial,  LLC as of  December  31,  2006  and for the
             period covered by this Form 10-K.
33.3.1       Report on Assessment of Compliance with Servicing  Criteria of HSBC
             Mortgage  Corporation  (USA) as of  December  31,  2006 and for the
             period covered by this Form 10-K.
33.3.2       Report on Assessment of Compliance with Servicing Criteria of First
             American  Real Estate  Solutions of Texas,  L.P. as of December 31,
             2006 and for the period covered by this Form 10-K.
33.4.1       Report on Assessment of Compliance with Servicing Criteria of
             Wells Fargo Home Mortgage, Inc. as of December 31, 2006 and for
             the period covered by this Form 10-K.
33.4.2       Report on  Assessment  of  Compliance  with  Servicing  Criteria of
             Regulus  Group  LLC as of  December  31,  2006  and for the  period
             covered by this Form 10-K.
33.4.3       Report on Assessment of Compliance with Servicing Criteria of ZC
             Sterling Insurance Agency, Inc. as of December 31, 2006 and for
             the period covered by this Form 10-K.
33.5         Report on Assessment of Compliance with Servicing  Criteria of U.S.
             Bank  National  Association  as of  December  31,  2006 and for the
             period covered by this Form 10-K.
33.6         Report on Assessment of Compliance with Servicing Criteria of Wells
             Fargo Bank,  National  Association  as of December 31, 2006 and for
             the period covered by this Form 10-K.
34.1         Attestation Report of  PricewaterhouseCoopers  LLP on Assessment of
             Compliance with Servicing Criteria relating to Residential  Funding
             Company, LLC.
34.2         Attestation Report of  PricewaterhouseCoopers  LLP on Assessment of
             Compliance   with  Servicing   Criteria   relating  to  Homecomings
             Financial, LLC.
34.3.1       Attestation  Report of KPMG LLP on Assessment  of  Compliance  with
             Servicing Criteria relating to HSBC Mortgage Corporation (USA).
34.3.2       Attestation Report of PricewaterhouseCoopers LLP on Assessment
             of Compliance with Servicing Criteria relating to First American
             Real Estate Solutions of Texas, L.P.
34.4.1       Attestation Report of KPMG LLP on Assessment of Compliance with
             Servicing Criteria relating to Wells Fargo Home Mortgage, Inc.
34.4.2       Attestation  Report of KPMG LLP on Assessment  of  Compliance  with
             Servicing Criteria relating to Regulus Group LLC.
34.4.3       Attestation Report of Ernst & Young LLP on Assessment of Compliance
             with Servicing  Criteria relating to ZC Sterling  Insurance Agency,
             Inc..
34.5         Attestation Report of Ernst & Young LLP on Assessment of
             Compliance with Servicing Criteria relating to U.S. Bank
             National Association.
34.6         Attestation Report of KPMG LLP on Assessment of Compliance with
             Servicing Criteria relating to Wells Fargo Bank, National
             Association.
35.1         Servicer Compliance Statement of Residential Funding Company,
             LLC.
35.2         Servicer Compliance Statement of GMAC Mortgage, LLC.
35.3         Servicer Compliance Statement of Homecomings Financial, LLC.
35.4         Servicer Compliance Statement of HSBC Mortgage Corporation (USA).