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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
 Washington, D.C. 20549
 FORM 10-K
 ANNUAL REPORT
PURSUANT TO SECTIONS 13 OR 15(d)
OF THE SECURITIES EXCHANGE ACT OF 1934
  þ
    
    ANNUAL REPORT PURSUANT TO SECTION 13 OR
15(d) OF THE
 SECURITIES EXCHANGE ACT OF
1934
 For
the fiscal year ended December 31, 2005
 OR
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    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 333-110499-173
 Principal
Life Income Fundings Trust 2005-78
 (by Principal Life Insurance Company as depositor)
  Iowa
(State or other jurisdiction of
incorporation or organization)
    
    42-0127290
(I.R.S. Employer Identification No.)
 Principal
Life Income Fundings Trust 2005-78
c/o Principal Life Insurance Company, as depositor
711 High Street
Des Moines, Iowa 50392-0001
(515) 247-5111
 (515) 247-5111
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TABLE OF CONTENTS  PART IItem 3. Legal ProceedingsItem 4. Submission of Matters to a Vote of Security HoldersPART IIItem 5. Market for Registrants Common Equity, Related Stockholder Matters and Issuer Purchases of Equity SecuritiesPART IIIItem 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder MattersItem 13. Certain Relationships and Related TransactionsPART IVItem 15. Exhibits, Financial Statement Schedules, and Reports on Form 8-KSIGNATURESEXHIBIT INDEXSection 302 CertificationAnnual Statement of ComplianceReport of Independent Registered Public Accounting Firm    Table of Contents  
 PART I
 
 Item 3. Legal Proceedings.
  
 Item 4. Submission of Matters to a Vote of Security Holders.
  
 PART II
 
 Item 5. Market for Registrants Common Equity, Related Stockholder Matters and Issuer Purchases of
Equity Securities.
 ® ®
 
 Principalâ is a registered service mark of Principal Financial Services, Inc.
and is used under license.

CoreNotesâ is a registered service mark of Merrill Lynch & Co., Inc. 2




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PART III
 
 Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder
Matters.
  
 Item 13. Certain Relationships and Related Transactions.
  
 PART IV
 
 Item 15. Exhibits, Financial Statement Schedules, and Reports on Form 8-K.
 Exhibit 31.1
    
    Section 302 Certification.Exhibit 99.1
    
    Indenture Trustee Report of the
Trust  Principal
Life Income Fundings Trust 2005-78 made no payment of interest or
principal on its 4.75% Principal®
Life CoreNotes®  due 2010 during the fiscal year
ended December 31, 2005.  As such, no Indenture Trustee Reports were prepared or are included in this Annual Report on Form 10K.Exhibit 99.2
    
    Annual Statement of Compliance by Citibank, N.A.Exhibit 99.3
    
    Report of Independent Registered Public Accounting Firm on Compliance.
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##### Table of Contents



SIGNATURES
  PRINCIPAL LIFE INSURANCE COMPANY
(Registrant)Date: March 24, 2006
    
    By:
    
    /s/Karen A. PearstonName: Karen A. PearstonTitle: Second Vice President and Counsel
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##### Table of Contents



EXHIBIT INDEX
 ExhibitNumber
    
    DescriptionExhibit 31.1
    
    Section 302 Certification.Exhibit 99.1
    
    Indenture Trustee Report of the
Trust  Principal Life Income
Fundings Trust 2005-78 made no payment of interest or principal on its 4.75%
Principal® Life CoreNotes®  due 2010
during the fiscal year ended December 31, 2005.  As such, no Indenture Trustee
Reports were prepared or are included in this Annual Report on Form 10K.Exhibit 99.2
    
    Annual Statement of Compliance by Citibank, N.A.Exhibit 99.3
    
    Report of Independent Registered Public Accounting Firm on Compliance.
 5