497

Exhibit Index

Exhibit No.
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	497
Document Period End Date	dei_DocumentPeriodEndDate	Dec. 31, 2017
Registrant Name	dei_EntityRegistrantName	STATE STREET INSTITUTIONAL INVESTMENT TRUST
Central Index Key	dei_EntityCentralIndexKey	0001107414
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Jun. 06, 2018
Document Effective Date	dei_DocumentEffectiveDate	Jun. 06, 2018
Prospectus Date	rr_ProspectusDate	Apr. 30, 2018

XML

Apr. 30, 2018

State Street Institutional Investment Trust

(the "Trust")

State Street Global Equity ex-U.S. Index Fund

(the "Fund")

Class A (SSGHX) Class I (SSGJX) Class K (SSGLX)

SUPPLEMENT DATED JUNE 6, 2018 TO THE

PROSPECTUS AND STATEMENT OF ADDITIONAL INFORMATION (the "SAI")

EACH DATED APRIL 30, 2018

Effective June 7, 2018 (the "Effective Date"), the contractual operating expense waiver for the Fund will be reduced, through April 30, 2020, from 0.10% to 0.015% of the Fund's average daily net assets on an annual basis.

Accordingly, on the Effective Date, the Prospectus is revised as follows:

The sub-sections within the Fund Summary entitled "Annual Fund Operating Expenses" on page 14 of the Prospectus and "Expenses" on page 15 of the Prospectus are each deleted in their entirety and replaced in each instance with the following:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)

	Class A			Class I			Class K
Management Fee		0.060	%		0.060	%		0.060	%
Distribution and/or Shareholder Service (12b-1) Fees		0.250	%		0.000	%		0.000	%
Other Expenses2		0.367	%		0.367	%		0.167	%
Total Annual Fund Operating Expenses		0.677	%		0.427	%		0.227	%
Less Fee Waivers and/or Expense Reimbursements3		(0.162	)%		(0.162	)%		(0.162	)%
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements		0.515	%		0.265	%		0.065	%

¹  A contingent deferred sales charge ("CDSC") of 1.00% may be assessed on redemptions of Class A shares made within 18 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $1,000,000 or more.

²  Other Expenses have been restated to reflect current fees for Class A and Class I shares.

³  The Fund's investment adviser, SSGA Funds Management, Inc. (the "Adviser" or "SSGA FM"), is contractually obligated until April 30, 2020 (i) to waive up to the full amount of the advisory fee payable by the Fund, and/or (ii) to reimburse the Fund for expenses to the extent that Total Annual Fund Operating Expenses (exclusive of non-recurring account fees, extraordinary expenses, acquired fund fees, administration fees and any class-specific expenses, such as distribution, shareholder servicing, and sub-transfer agency fees) exceed 0.015% of average daily net assets on an annual basis. This waiver and/or reimbursement may not be terminated prior to April 30, 2020 except with approval of the Fund's Board of Trustees.

Example

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated, and then sell all of your Fund Shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. The Example takes into account the effect of the Fund's contractual fee waiver and/or reimbursement through April 30, 2020. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	1 year		3 years		5 years		10 years
Class A	$	575	$	699	$	851	$	1,294
Class I	$	25	$	103	$	206	$	506
Class K	$	7	$	39	$	94	$	256

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

STATE STREET INSTITUTIONAL INVESTMENT TRUST

Prospectus Date

rr_ProspectusDate

Apr. 30, 2018

Supplement [Text Block]

ssiit_SupplementTextBlock

State Street Institutional Investment Trust

(the "Trust")

State Street Global Equity ex-U.S. Index Fund

(the "Fund")

Class A (SSGHX) Class I (SSGJX) Class K (SSGLX)

SUPPLEMENT DATED JUNE 6, 2018 TO THE

PROSPECTUS AND STATEMENT OF ADDITIONAL INFORMATION (the "SAI")

EACH DATED APRIL 30, 2018

Effective June 7, 2018 (the "Effective Date"), the contractual operating expense waiver for the Fund will be reduced, through April 30, 2020, from 0.10% to 0.015% of the Fund's average daily net assets on an annual basis.

Accordingly, on the Effective Date, the Prospectus is revised as follows:

The sub-sections within the Fund Summary entitled "Annual Fund Operating Expenses" on page 14 of the Prospectus and "Expenses" on page 15 of the Prospectus are each deleted in their entirety and replaced in each instance with the following:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)

	Class A			Class I			Class K
Management Fee		0.060	%		0.060	%		0.060	%
Distribution and/or Shareholder Service (12b-1) Fees		0.250	%		0.000	%		0.000	%
Other Expenses2		0.367	%		0.367	%		0.167	%
Total Annual Fund Operating Expenses		0.677	%		0.427	%		0.227	%
Less Fee Waivers and/or Expense Reimbursements3		(0.162	)%		(0.162	)%		(0.162	)%
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements		0.515	%		0.265	%		0.065	%

¹  A contingent deferred sales charge ("CDSC") of 1.00% may be assessed on redemptions of Class A shares made within 18 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $1,000,000 or more.

²  Other Expenses have been restated to reflect current fees for Class A and Class I shares.

³  The Fund's investment adviser, SSGA Funds Management, Inc. (the "Adviser" or "SSGA FM"), is contractually obligated until April 30, 2020 (i) to waive up to the full amount of the advisory fee payable by the Fund, and/or (ii) to reimburse the Fund for expenses to the extent that Total Annual Fund Operating Expenses (exclusive of non-recurring account fees, extraordinary expenses, acquired fund fees, administration fees and any class-specific expenses, such as distribution, shareholder servicing, and sub-transfer agency fees) exceed 0.015% of average daily net assets on an annual basis. This waiver and/or reimbursement may not be terminated prior to April 30, 2020 except with approval of the Fund's Board of Trustees.

Example

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated, and then sell all of your Fund Shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. The Example takes into account the effect of the Fund's contractual fee waiver and/or reimbursement through April 30, 2020. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	1 year		3 years		5 years		10 years
Class A	$	575	$	699	$	851	$	1,294
Class I	$	25	$	103	$	206	$	506
Class K	$	7	$	39	$	94	$	256

State Street Global Equity ex-U.S. Index Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement [Text Block]

ssiit_SupplementTextBlock

State Street Institutional Investment Trust

(the "Trust")

State Street Global Equity ex-U.S. Index Fund

(the "Fund")

Class A (SSGHX) Class I (SSGJX) Class K (SSGLX)

SUPPLEMENT DATED JUNE 6, 2018 TO THE

PROSPECTUS AND STATEMENT OF ADDITIONAL INFORMATION (the "SAI")

EACH DATED APRIL 30, 2018

Effective June 7, 2018 (the "Effective Date"), the contractual operating expense waiver for the Fund will be reduced, through April 30, 2020, from 0.10% to 0.015% of the Fund's average daily net assets on an annual basis.

Accordingly, on the Effective Date, the Prospectus is revised as follows:

The sub-sections within the Fund Summary entitled "Annual Fund Operating Expenses" on page 14 of the Prospectus and "Expenses" on page 15 of the Prospectus are each deleted in their entirety and replaced in each instance with the following:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)

	Class A			Class I			Class K
Management Fee		0.060	%		0.060	%		0.060	%
Distribution and/or Shareholder Service (12b-1) Fees		0.250	%		0.000	%		0.000	%
Other Expenses2		0.367	%		0.367	%		0.167	%
Total Annual Fund Operating Expenses		0.677	%		0.427	%		0.227	%
Less Fee Waivers and/or Expense Reimbursements3		(0.162	)%		(0.162	)%		(0.162	)%
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements		0.515	%		0.265	%		0.065	%

¹  A contingent deferred sales charge ("CDSC") of 1.00% may be assessed on redemptions of Class A shares made within 18 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $1,000,000 or more.

²  Other Expenses have been restated to reflect current fees for Class A and Class I shares.

³  The Fund's investment adviser, SSGA Funds Management, Inc. (the "Adviser" or "SSGA FM"), is contractually obligated until April 30, 2020 (i) to waive up to the full amount of the advisory fee payable by the Fund, and/or (ii) to reimburse the Fund for expenses to the extent that Total Annual Fund Operating Expenses (exclusive of non-recurring account fees, extraordinary expenses, acquired fund fees, administration fees and any class-specific expenses, such as distribution, shareholder servicing, and sub-transfer agency fees) exceed 0.015% of average daily net assets on an annual basis. This waiver and/or reimbursement may not be terminated prior to April 30, 2020 except with approval of the Fund's Board of Trustees.

Example

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated, and then sell all of your Fund Shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. The Example takes into account the effect of the Fund's contractual fee waiver and/or reimbursement through April 30, 2020. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	1 year		3 years		5 years		10 years
Class A	$	575	$	699	$	851	$	1,294
Class I	$	25	$	103	$	206	$	506
Class K	$	7	$	39	$	94	$	256

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2020

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

A contingent deferred sales charge (“CDSC”) of 1.00% may be assessed on redemptions of Class A shares made within 18 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $1,000,000 or more.

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Other Expenses have been restated to reflect current fees for Class A and Class I shares.

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated, and then sell all of your Fund Shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. The Example takes into account the effect of the Fund’s contractual fee waiver and/or reimbursement through April 30, 2020. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

State Street Global Equity ex-U.S. Index Fund | Class A

Risk/Return:

rr_RiskReturnAbstract

Management Fee

rr_ManagementFeesOverAssets

0.06%

Distribution and/or Shareholder Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.367%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.677%

Less Fee Waivers and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.162%)

^[2]

Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements

rr_NetExpensesOverAssets

0.515%

1 year

rr_ExpenseExampleYear01

$ 575

3 years

rr_ExpenseExampleYear03

699

5 years

rr_ExpenseExampleYear05

851

10 years

rr_ExpenseExampleYear10

$ 1,294

State Street Global Equity ex-U.S. Index Fund | Class I

Risk/Return:

rr_RiskReturnAbstract

Management Fee

rr_ManagementFeesOverAssets

0.06%

Distribution and/or Shareholder Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.367%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.427%

Less Fee Waivers and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.162%)

^[2]

Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements

rr_NetExpensesOverAssets

0.265%

1 year

rr_ExpenseExampleYear01

$ 25

3 years

rr_ExpenseExampleYear03

103

5 years

rr_ExpenseExampleYear05

206

10 years

rr_ExpenseExampleYear10

$ 506

State Street Global Equity ex-U.S. Index Fund | Class K

Risk/Return:

rr_RiskReturnAbstract

Management Fee

rr_ManagementFeesOverAssets

0.06%

Distribution and/or Shareholder Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.167%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.227%

Less Fee Waivers and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.162%)

^[2]

Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements

rr_NetExpensesOverAssets

0.065%

1 year

rr_ExpenseExampleYear01

$ 7

3 years

rr_ExpenseExampleYear03

39

5 years

rr_ExpenseExampleYear05

94

10 years

rr_ExpenseExampleYear10

$ 256

[1] Other Expenses have been restated to reflect current fees for Class A and Class I shares.

[2] The Fund’s investment adviser, SSGA Funds Management, Inc. (the “Adviser” or “SSGA FM”), is contractually obligated until April 30, 2020 (i) to waive up to the full amount of the advisory fee payable by the Fund, and/or (ii) to reimburse the Fund for expenses to the extent that Total Annual Fund Operating Expenses (exclusive of non-recurring account fees, extraordinary expenses, acquired fund fees, administration fees and any class-specific expenses, such as distribution, shareholder servicing, and sub-transfer agency fees) exceed 0.015% of average daily net assets on an annual basis. This waiver and/or reimbursement may not be terminated prior to April 30, 2020 except with approval of the Fund’s Board of Trustees.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	STATE STREET INSTITUTIONAL INVESTMENT TRUST
Prospectus Date	rr_ProspectusDate	Apr. 30, 2018
Document Creation Date	dei_DocumentCreationDate	Jun. 06, 2018