UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM N-Q

QUARTERLY SCHEDULE OF PORTFOLIO HOLDINGS OF REGISTERED
MANAGEMENT INVESTMENT COMPANY

Investment Company Act file number 811-10333

Name of Fund: BlackRock Municipal Income Investment Trust (BBF)

Fund Address: 100 Bellevue Parkway, Wilmington, DE 19809

Name and address of agent for service: Donald C. Burke, Chief Executive Officer, BlackRock Municipal Income Investment Trust, 800 Scudders Mill Road, Plainsboro, NJ, 08536. Mailing address: P.O. Box 9011, Princeton, NJ, 08543-9011

Registrant’s telephone number, including area code: (800) 882-0052, Option 4

Date of fiscal year end: 07/31/2009

Date of reporting period: 08/01/2008 – 10/31/2008

Item 1 – Schedule of Investments

BlackRock Municipal Income Investment Trust    
Schedule of Investments October 31, 2008 (Unaudited)   (Percentages shown are based on Net Assets)
            Par      
State   Municipal Bonds   (000)     Value
Florida - 138%   Ave Maria Stewardship Community District, Florida, Revenue Bonds,          
    4.80%, 11/01/12
$
1,000                   $ 866,020
    Beacon Tradeport Community Development District, Florida, Special          
    Assessment Revenue Refunding Bonds (Commercial Project), Series A,          
    5.625%, 5/01/32 (a)   7,705     6,586,234
    Brevard County, Florida, Health Facilities Authority, Healthcare Facilities          
    Revenue Bonds (Health First, Inc. Project), 5%, 4/01/36   2,000     1,251,640
    Broward County, Florida, School Board, COP, Series A, 5.25%, 7/01/33 (b)   1,700     1,546,949
    Capital Projects Finance Authority, Florida, Student Housing          
    Revenue Bonds (Capital Projects Loan Program),          
    Senior Series F-1, 5%, 10/01/31 (c)   2,800     2,370,508
    Capital Region Community Development District, Florida, Special          
    Assessment Revenue Bonds, Series A, 7%, 5/01/39   640     538,976
    Escambia County, Florida, Health Facilities Authority, Health Facility          
    Revenue Bonds (Florida Health Care Facility Loan), 5.95%, 7/01/20 (d)   799     806,761
    Fort Myers, Florida, Utility System Revenue Refunding          
    Bonds, 5%, 10/01/31 (c)   1,355     1,240,909
    Halifax Hospital Medical Center, Florida, Hospital Revenue Refunding and          
    Improvement Bonds, Series A, 5.25%, 6/01/26   2,500     1,975,900
    Heritage Harbour North Community Development District, Florida, Capital          
    Improvement Bonds, 6.375%, 5/01/38   1,500     1,113,105
    Heritage Harbour South Community Development District, Florida, Capital          
    Improvement Special Assessment Bonds, Series A, 6.50%, 5/01/34   1,610     1,348,971
    Highlands County, Florida, Health Facilities Authority, Hospital Revenue          
    Bonds (Adventist Health System), Series A, 6%, 11/15/11 (e)   6,500     7,115,680
    Hillsborough County, Florida, IDA, PCR, Refunding (Tampa Electric Company          
    Project), 5.50%, 10/01/23   1,450     1,196,699
    Hillsborough County, Florida, IDA, PCR, Refunding (Tampa Electric Company          
    Project), Series A, 5.65%, 5/15/18   900     839,853
    Jacksonville, Florida, Health Facilities Authority, Hospital Revenue Bonds          
    (Baptist Medical Center Project), 5%, 8/15/37 (b)   2,280     1,994,362
    Jacksonville, Florida, Sales Tax Revenue Bonds, 5%, 10/01/30   4,085     3,645,086
    Jacksonville, Florida, Transit Revenue Bonds, 5%, 10/01/26 (c)   4,000     3,786,800
    Laguna Lakes Community Development District, Florida, Special Assessment          
    Revenue Refunding Bonds, Series A, 6.40%, 5/01/13 (e)   1,575     1,768,032
    Lee County, Florida, IDA, Health Care Facilities, Revenue Refunding Bonds          
    (Shell Point/Alliance Obligor Group), 5%, 11/15/32   1,430     917,617
    Lee Memorial Health System, Florida, Hospital Revenue Bonds,          
    Series A, 5%, 4/01/32 (d)   1,000     878,450
Portfolio Abbreviations              

To simplify the listings of the portfolio holdings in the Schedule of Investments, the names and descriptions of many of the securities have abbreviated according to the list below.

AMT   Alternative Minimum Tax (subject to)   IDA   Industrial Development Authority
CABS   Capital Appreciation Bonds   IDR   Industrial Development Revenue Bonds
COP   Certificates of Participation   PCR   Pollution Control Revenue Bonds
GO   General Obligation Bonds        

1

BlackRock Municipal Income Investment Trust    
Schedule of Investments October 31, 2008 (Unaudited)   (Percentages shown are based on Net Assets)
        Par      
State   Municipal Bonds   (000)     Value
                                      
Madison County, Florida, First Mortgage Revenue Bonds (Twin Oaks Project),
         
    Series A, 6%, 7/01/25
$
1,620                   $ 1,289,828
    Melbourne, Florida, Water and Sewer Revenue Bonds,          
    5.23%, 10/01/21 (f)(g)(h)   2,770     1,395,304
    Miami Beach, Florida, Health Facilities Authority, Hospital Revenue          
    Refunding Bonds (Mount Sinai Medical Center of Florida),          
    6.75%, 11/15/21   1,565     1,309,389
    Miami-Dade County, Florida, Expressway Authority, Toll System Revenue          
    Refunding Bonds, 5.125%, 7/01/25 (c)(f)   1,000     961,450
    Miami-Dade County, Florida, School Board, COP, Refunding,          
    Series B, 5.25%, 5/01/28 (i)   1,440     1,379,016
    Miami-Dade County, Florida, School Board, COP, Refunding,          
    Series B, 5.25%, 5/01/30 (i)   1,160     1,101,281
    Miami-Dade County, Florida, Special Obligation Revenue Bonds,          
    Sub-Series B, 5.596%, 10/01/33 (c)(h)   9,700     1,846,298
    Miami-Dade County, Florida, Special Obligation Revenue Bonds,          
    Sub-Series C, 5.623%, 10/01/28 (c)(h)   25,000     6,793,500
    Miami-Dade County, Florida, Special Obligation Revenue Refunding Bonds,          
    Sub-Series A, 5.535%, 10/01/19 (c)(h)   2,595     1,355,965
    New River Community Development District, Florida, Capital Improvement          
    Revenue Bonds, Series B, 5%, 5/01/13   1,500     948,945
    Northern Palm Beach County Improvement District, Florida,          
    Water Control and Improvement Revenue Bonds (Unit of Development          
    Number 43), 6.10%, 8/01/11 (e)   1,155     1,239,026
    Northern Palm Beach County Improvement District, Florida, Water Control          
   
and Improvement Revenue Bonds (Unit of Development Number 43), 6.125%,
         
    8/01/11 (e)   3,500     3,831,660
    Northern Palm Beach County Improvement District, Florida,          
    Water Control and Improvement Revenue Bonds (Unit of Development          
    Number 43), 6.10%, 8/01/21   225     201,092
    Orange County, Florida, Educational Facilities Authority, Educational          
    Facilities Revenue Bonds (Rollins College Project), 5.25%, 12/01/27 (d)   1,000     932,600
    Orange County, Florida, Health Facilities Authority, Health Care Revenue          
    Refunding Bonds (Orlando Lutheran Towers), 5.375%, 7/01/20   655     491,021
    Orange County, Florida, Health Facilities Authority, Hospital Revenue Bonds          
    (Orlando Regional Healthcare), 5.70%, 7/01/26   600     425,952
    Orange County, Florida, Health Facilities Authority, Hospital Revenue          
    Refunding Bonds (Orlando Regional Healthcare), Series B,          
    5.25%, 12/01/29 (b)   1,200     1,138,392
    Orange County, Florida, Tourist Development, Tax Revenue Refunding          
    Bonds, 5%, 10/01/29 (d)   1,300     1,146,184
    Orlando, Florida, Senior Tourist Development Tax Revenue Bonds (6th Cent          
    Contract Payments), Series A, 5.25%, 11/01/38 (i)   1,000     906,490
    Orlando-Orange County Expressway Authority, Florida, Expressway Revenue          
    Bonds, Series A, 5%, 7/01/32 (b)   2,000     1,809,560
    Palm Beach County, Florida, School Board, COP, Refunding,          
    Series B, 5%, 8/01/25 (d)   2,500     2,277,300

2

BlackRock Municipal Income Investment Trust    
Schedule of Investments October 31, 2008 (Unaudited)  
(Percentages shown are based on Net Assets)
        Par      
State   Municipal Bonds   (000)     Value
        Pine Ridge Plantation Community Development District, Florida, Capital          
    Improvement and Special Assessment Bonds, Series B, 5%, 5/01/11
$
580                   $ 532,092
    Saint Johns County, Florida, Ponte Vedra Utility System Revenue Bonds,          
    5%, 10/01/35 (b)   1,000     875,650
   
Saint Johns County, Florida, Water and Sewer Revenue Bonds, CABS, 5.335%,
         
    6/01/30 (d)(h)   3,945     993,943
    South Miami Health Facilities Authority, Florida, Hospital Revenue Bonds          
    (Baptist Health System Obligation Group), 5.25%, 2/01/13 (e)   12,000     12,930,120
   
South Miami Health Facilities Authority, Florida, Hospital Revenue Refunding
         
    Bonds (Baptist Health System Obligation Group), 5%, 8/15/32   1,000     814,340
    Sumter County, Florida, IDA, IDR (North Sumter Utility Company LLC), AMT,          
    6.80%, 10/01/32   2,655     2,267,768
    Suncoast Community Development District, Florida, Capital Improvement          
    Revenue Bonds, Series A, 5.875%, 5/01/34   985     758,755
    Tampa, Florida, Revenue Bonds (University of Tampa Project),          
    5.625%, 4/01/32 (a)   5,500     4,640,515
    Tampa, Florida, Water and Sewer Revenue Refunding Bonds,          
    Series A, 5%, 10/01/26   4,000     3,862,080
    Tolomato Community Development District, Florida, Special Assessment          
    Bonds, 6.55%, 5/01/27   1,250     1,039,863
    Village Center Community Development District, Florida, Recreational          
    Revenue Bonds, Series A, 5%, 11/01/32 (c)   1,795     1,504,695
    Village Community Development District Number 5, Florida, Special          
    Assessment Bonds, Series A, 6%, 5/01/22   2,765     2,406,075
    Village Community Development District Number 5, Florida, Special          
    Assessment Bonds, Series A, 6.50%, 5/01/33   1,325     1,112,921
    Volusia County, Florida, Educational Facility Authority, Educational          
    Facilities Revenue Bonds (Embry-Riddle Aeronautical University Project),          
    Series A, 5.75%, 10/15/29   2,000     1,645,740
    Watergrass Community Development District, Florida, Special Assessment          
    Revenue Bonds, Series B, 5.125%, 11/01/14   1,000     833,540
              110,786,902
Nevada - 3.2%   Clark County, Nevada, Water Reclamation District, Limited          
    Tax, GO, 6%, 7/01/38   2,500     2,545,625
New York - 1.7%   New York City, New York, City Municipal Water Finance Authority, Water          
    and Sewer System Revenue Bonds, Series A, 5.75%, 6/15/40   1,400     1,395,436
South Carolina - 2.1%   South Carolina State Public Service Authority, Revenue Refunding Bonds,          
    Series A, 5.50%, 1/01/38   1,750     1,669,325
Texas - 1.5%   North Texas Tollway Authority, System Revenue Refunding Bonds, First Tier,          
    Series K-1, 5.75%, 1/01/38 (i)   1,250     1,205,425
Puerto Rico - 2.3%   Puerto Rico Commonwealth Aqueduct and Sewer Authority, Senior Lien          
    Revenue Bonds, Series A, 6%, 7/01/44   2,100     1,867,068
    Total Municipal Bonds - 148.8%         119,469,781
    Municipal Bonds Transferred to          
    Tender Option Bond Trusts (j)          
Florida - 9.4%   Jacksonville Electric Authority, Florida, Saint John's River Power Park          
    System Revenue Bonds, Issue Three, Series 2, 5%, 10/01/37    
1,110
 
974,913
 

3

BlackRock Municipal Income Investment Trust    
Schedule of Investments October 31, 2008 (Unaudited)  
(Percentages shown are based on Net Assets)
        Par      
State   Municipal Bonds   (000)     Value
                                    Jacksonville, Florida, Economic Development Commission, Health Care                    
    Facilities Revenue Bonds (Mayo Clinic-Jacksonville),          
    Series B, 5.50%, 11/15/36  
$      7,493
 
$     
6,609,763 
    Total Municipal Bonds Transferred to          
    Tender Option Bond Trusts - 9.4%         7,584,676 
    Total Long-Term Investments (Cost - $140,127,400) - 158.2%       127,054,457 
    Short-Term Securities   Shares      
    CMA Florida Municipal Money Fund, 1.20% (k)(l)  
11,720,185
    11,720,185 
    Total Short-Term Securities (Cost - $11,720,185) - 14.6%         11,720,185 
    Total Investments (Cost - $151,847,585*) - 172.8%       138,774,642 
    Liabilities in Excess of Other Assets - (4.1)%         (3,298,011)
    Liability for Trust Certificates, Including Interest Expense          
         and Fees Payable - (7.0)%         (5,619,156)
    Preferred Shares, at Redemption Value - (61.7)%       (49,570,954)
    Net Assets Applicable to Common Shares - 100.0%      
$     
80,286,521 

*        

The cost and unrealized appreciation (depreciation) of investments as of October 31, 2008, as computed for federal income tax purposes, were as follows:
 
Aggregate cost                                                                   $            145,685,423  
Gross unrealized appreciation   $ 2,812,688  
Gross unrealized depreciation     (15,271,657
)
Net unrealized depreciation   $ (12,458,969
)

(a)     

Radian Insured.
(b)     

FSA Insured.
(c)     

MBIA Insured.
(d)     

AMBAC Insured.
(e)     

U.S. government securities, held in escrow, are used to pay interest on this security as well as to retire the bond in full at the date indicated, typically at a premium to par.
(f)     

FGIC Insured.
(g)     

Security is collateralized by Municipal or U.S. Treasury Obligations.
(h)     

Represents a zero-coupon bond. The interest rate shown is the effective yield at the time of purchase.
(i)     

Assured Guaranty Insured.
(j)     

Securities represent bonds transferred to a tender option bond trust in exchange for which the Trust acquired residual interest certificates. These securities serve as collateral in a financing transaction.
(k)     

Represents the current yield as of report date.
(l)     

Investments in companies considered to be an affiliate of the Trust, for purposes of Section 2(a)(3) of the Investment Company Act of 1940, were as follows:
 
 
 
      Net        
  Affiliate   Activity      
Income
  CMA Florida Municipal Money Fund   5,216,852      
$  39,136

4

BlackRock Municipal Income Investment Trust
Schedule of Investments October 31, 2008 (Unaudited)

  • Effective August 1, 2008, the Trust adopted Financial Accounting Standards Board Statement of Financial Accounting Standards No. 157, "Fair Value Measurements" ("FAS 157"). FAS 157 clarifies the definition of fair value, establishes a framework for measuring fair values and requires additional disclosures about the use of fair value measurements. Various inputs are used in determining the fair value of investments, which are as follows:

  • Level 1 - price quotations in active markets/exchanges for identical securities

  • Level 2 - other observable inputs (including, but not limited to: quoted prices for similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the assets or liabilities (such as interest rates, yield curves, volatilities, prepayment speeds, loss severities, credit risks, and default rates) or other market-corroborated inputs)

  • Level 3 - unobservable inputs based on the best information available in the circumstance, to the extent observable inputs are not available (including the Trust's own assumption used in determining the fair value of investments)

The inputs or methodology used for valuing securities are not necessarily an indication of the risk associated with investing in those securities. For information about the Trust's policy regarding valuation of investments and other significant accounting policies, please refer to the Trust's most recent financial statements as contained in its annual report.

The following table summarizes the inputs used as of October 31, 2008 in determining the fair valuation of the Trust's investments:

 
Valuation     Investments in
Inputs     Securities
Level 1                         $ 11,720,185
Level 2     127,054,457
Level 3     -
Total   $ 138,774,642

 

 

5

Item 2 – Controls and Procedures

2(a) –     The registrant’s principal executive and principal financial officers or persons performing similar functions have concluded that the registrant’s disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940, as amended (the “1940 Act”)) are effective as of a date within 90 days of the filing of this report based on the evaluation of these controls and procedures required by Rule 30a-3(b) under the 1940 Act and Rule 13a-15(b) under the Securities Exchange Act of 1934, as amended.

2(b) –     There were no changes in the registrant’s internal control over financial reporting (as defined in Rule 30a-3(d) under the 1940 Act) that occurred during the registrant’s last fiscal quarter that have materially affected, or are reasonably likely to materially affect, the registrant’s internal control over financial reporting.

Item 3 – Exhibits

Certifications – Attached hereto

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

BlackRock Municipal Income Investment Trust

By:      /s/ Donald C. Burke
  Donald C. Burke
  Chief Executive Officer of
  BlackRock Municipal Income Investment Trust       

Date: December 19, 2008

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

By:      /s/ Donald C. Burke
  Donald C. Burke
  Chief Executive Officer (principal executive officer) of
 
BlackRock Municipal Income Investment Trust

Date: December 19, 2008

By:      /s/ Neal J. Andrews
  Neal J. Andrews
  Chief Financial Officer (principal financial officer) of
 
BlackRock Municipal Income Investment Trust

Date: December 19, 2008