485BPOS

Filed with the U.S. Securities and Exchange Commission on December 19, 2012

File Nos. 33-73792

811-08270

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933		[X]
Pre-Effective Amendment No.		[   ]
Post-Effective Amendment No.	46	[X]

and/or

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940		[X]
Amendment No.	49	[X]

(Check appropriate box or boxes)

RAINIER INVESTMENT MANAGEMENT MUTUAL FUNDS

(Exact name of Registrant as Specified in Charter)

601 Union Street, Suite 2801

Seattle, WA 98101

(Address of Principal Executive Office, including Zip Code)

(206) 518-6600

(Registrant’s Telephone Number, including Area Code)

Melodie B. Zakaluk

Rainier Investment Management, Inc.

601 Union Street, Suite 2801

Seattle, WA 98101

(Name and address of Agent for Service)

WITH COPY TO:

David A. Hearth

Paul Hastings LLP

55 Second Street, 24^th Floor

San Francisco, CA 94105

It is proposed that this filing will become effective (check appropriate box)

[X]	Immediately upon filing pursuant to Rule 485(b)
[   ]	on (date) pursuant to Rule 485(b)
[   ]	60 days after filing pursuant to Rule 485 (a)(1)
[   ]	on (date) pursuant to Rule 485(a)(1)
[   ]	75 days after filing pursuant to Rule 485 (a)(2)
[   ]	on (date) pursuant to Rule 485(a)(2).

If appropriate, check the following box:

[   ] This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

Explanatory Note: This Post-Effective Amendment (“PEA”) No. 46 to the Registration Statement of Rainier Investment Management Mutual Funds on Form N-1A hereby incorporates Parts A, B and C from the Trust’s PEA No. 45 on Form N-1A filed on November 30, 2012. This PEA No. 46 is filed for the sole purpose of submitting the XBRL exhibit for the risk return summary first provided in PEA No. 45 to the Trust’s Registration Statement for its series: Rainier International Discovery Fund.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended (the “Securities Act”) and the Investment Company Act of 1940, as amended, the Registrant certifies that it meets all of the requirements for effectiveness of this Registration Statement under Rule 485(b) under the Securities Act and has duly caused Post-Effective Amendment No. 46 to this registration statement to be signed on its behalf by the undersigned, duly authorized, in the City of Seattle, State of Washington, on the 19th day of December, 2012.

RAINIER INVESTMENT MANAGEMENT MUTUAL FUNDS

/s/ Melodie B. Zakaluk                            

Melodie B. Zakaluk

Chief Executive Officer, President,

Chief Financial Officer and Treasurer

Pursuant to the requirements of the Securities Act, this Amendment to the Registration Statement on Form N-1A has been signed below by the following person in the capacities and on the date indicated.

Signature	Title	Date
/s/ Melodie B. Zakaluk	Trustee, Chief Executive Officer, President, Chief Financial Officer and Treasurer	December 19, 2012
Melodie B. Zakaluk
/s/ Gary L. Sundem*   Gary L. Sundem	Trustee	December 19, 2012
/s/ James E. Diamond, Jr.*   James E. Diamond, Jr.	Trustee	December 19, 2012
Joan L. Enticknap	Trustee

  * By /s/ Melodie B. Zakaluk

Melodie B. Zakaluk

Chief Executive Officer,

President,

Chief Financial Officer and Treasurer, Attorney-in-fact pursuant to the power of attorney filed on July 29, 2011.

C-1

EXHIBIT LIST

Exhibit	Exhibit No.
Instance Document	EX-101.INS
Schema Document	EX-101.SCH
Calculation Linkbase Document	EX-101.CAL
Definition Linkbase Document	EX-101.DEF
Label Linkbase Document	EX-101.LAB
Presentation Linkbase Document	EX-101.PRE

C-2

XML

Rainier International Discovery Fund

Rainier International Discovery Fund
Class A Shares

INVESTMENT OBJECTIVE

The Rainier International Discovery Fund (the “International Discovery Fund” or “Fund”) seeks long-term capital appreciation.

FEES AND EXPENSES OF THE FUND

The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $25,000 in the Rainier Funds. More information about these and other discounts is available from your financial professional and in the section titled “Purchasing Shares” on page 15 of the Prospectus and “Additional Purchase and Redemption Information” on page B-37 of the Fund’s Statement of Additional Information.

Shareholder Fees
(fees paid directly from your investment)

Shareholder Fees		Rainier International Discovery Fund Class A Shares
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)		5.75%
Maximum Deferred Sales Charge (Load)	[1]	none
Maximum Sales Charge (Load) on Reinvested Dividends		none
Redemption or Exchange Fee		none

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

Annual Fund Operating Expenses		Rainier International Discovery Fund Class A Shares
Management Fees		1.00%
Distribution and Service (12b-1) Fees		0.25%
Other Expenses	[1]	1.12%
Total Annual Fund Operating Expenses		2.37%
Fee Reduction and/or Expense Reimbursement		(0.87%)
Total Annual Fund Operating Expenses After Fee Reduction and/or Expense Reimbursement	[2]	1.50%

EXAMPLE

This example is intended to help you compare the cost of investing in shares of 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 redeem all of your 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 (taking into account the contractual expense limitation in the first year). Although your actual cost may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	1 Year	3 Years
Rainier International Discovery Fund Class A Shares	719	1,133

PORTFOLIO TURNOVER

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal period from March 28, 2012 through March 31, 2012, the Fund’s turnover rate was 0.23% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

Under normal conditions the Fund will invest primarily in equity securities of companies that are small- to medium-sized at the time of purchase and are located in foreign developed countries and emerging market countries and that have strong earnings prospects relative to their peers and attractive overall business fundamentals. The portfolio manager selects stocks of companies he believes will increase in value over time and makes investment decisions based primarily on an analysis of individual companies, rather than on broad economic forecasts. The portfolio manager believes that, over the long term, stock price movements follow growth in earnings, revenues and/or cash flow. In normal market conditions, the Fund’s portfolio will primarily consist of securities of companies whose earnings or revenues are not only growing, but growing at an accelerating pace.

The Investment Adviser refers to its stock selection philosophy as Growth at a Reasonable Price (“GARP”). Stock selection focuses on companies that are likely to demonstrate superior earnings growth relative to their peers, and whose equities are selling at attractive relative valuations. In pursuing its investment objective, the Fund may invest in equity securities, including common stock and preferred stock, and securities convertible into common stock, including warrants, convertible bonds, and rights. In addition, the Fund may also invest in the initial public offerings (“IPOs”) of small-cap companies, real estate investment trusts (“REITs”) and similar types of investments outside of the U.S., and in certain derivatives including futures, options, forward contracts and participatory notes. Participatory notes allow investors, such as the Fund, to invest indirectly in foreign securities without registering in those foreign markets where the country requires registration to make any direct investment in securities. The Fund will generally not invest more than 25% of its net assets in participatory notes at the time of purchase.

The Fund will invest primarily in foreign securities, including American Depositary Receipts (“ADRs”), Global Depositary Receipts (“GDRs”), International Depositary Receipts (“IDRs”), U.S. dollar-denominated foreign securities and direct foreign securities (purchased on foreign exchanges). An IDR is a negotiable, bank-issued certificate representing ownership of stock securities by an investor outside the country of origin. An IDR is the non-U.S. equivalent of an ADR. The Fund is not required to invest a specified portion of its net assets in any particular geographic region or any particular industry or sector, but will typically invest in at least three foreign countries at any time. The Fund will generally not invest more than 50% of its net assets in issuers located in emerging markets.

The Fund is diversified and will generally hold between 60 and 120 securities and seeks to invest in securities that are selling at reasonable valuations. The Fund may sell a security, if it achieves the valuation target, or the underlying fundamentals deteriorate as compared to the portfolio manager’s expectations, or when it is replaced with a more attractive security.

In addition, up to 10% of the Fund’s net assets may be held in cash or cash equivalents at the Investment Adviser’s discretion.

PRINCIPAL INVESTMENT RISKS

Because the Fund invests in securities that normally experience daily price changes, there is the risk that an investor could lose money. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. The following risks could affect the value of your investment:

• Foreign Securities and Emerging Markets Risks – Investing in foreign securities and securities of companies located in emerging market countries involve additional risks as compared to investing in U.S. securities, including risks related to currency- exchange rate fluctuations, political and economic instability, differences in financial reporting, accounting, auditing and legal standards, nationalization, expropriation or confiscatory taxation, less-strict regulation of securities markets, less liquidity, more volatility, higher transaction costs, and delays in settling securities transactions. Investing in securities of companies located in emerging market countries involves even greater risk and volatility than investing in more developed foreign markets because of, among other things, smaller securities markets, higher transaction costs, and fixed or managed currencies.

• Growth Stock Risk – Growth stocks may fall out of favor with investors. Because growth stocks can have relatively high valuations, an investment in a growth stock can be more risky than an investment in a company with more modest growth expectations.

• IPO Risk – IPO share prices can be volatile and fluctuate considerably due to factors such as the absence of a prior public market, unseasoned trading, a limited number of shares available for trading, and limited operating history and/or information about the issuer. The purchase of IPO shares may involve high transaction costs. IPO shares are subject to market risk and liquidity risk. When the Fund’s asset base is small, investment in IPO shares could have a magnified impact on the performance of the Fund.

• Market Risk – The securities markets could decline or companies represented in the Fund may weaken or otherwise not meet market expectations. The securities markets have been subject to significant volatility recently which has increased the risks associated with an investment in the Fund.

• Management Risk – Like all managed funds, there is risk that the Investment Adviser’s strategy for managing the Fund may not achieve the desired results or may be less effective than other strategies in a particular market environment.

• Government Sponsored Entities Risk – Securities issued or guaranteed by government-sponsored entities may not be guaranteed or insured by the United States Government, and may only be supported by the credit of the issuing agency.

• New Fund Risk – There can be no guarantee that the Fund will grow to or maintain an economically viable size.

• Participatory Notes Risk – Investments in participatory notes involve risks normally associated with a direct investment in the underlying securities. In addition, participatory notes are subject to counterparty risk, which is the risk that the broker-dealer or bank that issues the participatory notes will not fulfill its contractual obligation to complete the transaction with the Fund.

• Real Estate Securities Risk – The value of a REIT and similar U.S. and foreign investments can be negatively affected by economic downturns or by changes in real estate values, rents, property taxes, interest rates, tax treatment, regulations, or the legal structure of the entity.

• Small-Cap Company Risk – Investments in securities of small-cap companies involve greater risk of loss than investing in larger, more established companies. Small-cap companies may have limited product lines, markets or financial resources and less seasoned management teams and may trade less frequently and at a lower volume than more widely held securities. The prices of small-cap companies’ stock tend to fluctuate in value more than other stocks.

• Derivatives Risk – The prices of derivatives may move in unexpected ways due to the use of leverage and other factors and may result in increased volatility or losses. The Fund may not be able to terminate or sell derivative positions, and a liquid secondary market may not always exist for derivative positions. The use of derivatives may also involve the risk that a counterparty to a derivative contract will fail to comply with the terms of the contract which could cause the Fund to lose its investment in the derivative instrument.

PERFORMANCE

Because the Fund does not have a full calendar year of performance to compare against a broad measure of market performance, performance information is not provided here. Performance information will be available after the Fund has been in operation for one calendar year. At that time, the performance information will provide some indication of the risks of investing in the Fund by comparing it against a broad measure of market performance.

[1] If no initial sales charge was assessed in certain circumstances, such as on a purchase of $1 million or more, a contingent deferred sales charge of 1.00% of the lesser of the initial offering price of the shares redeemed or the amount redeemed within one year of purchase may be assessed.

[1] Other Expenses are based on estimated amounts for the current fiscal year and include 0.31% for organizational costs which cover various one-time costs related to starting up the Fund.

[2] The Investment Adviser has contractually agreed to reduce its fees and/or pay Fund expenses (excluding Acquired Fund Fees and Expenses, interest, taxes, brokerage commissions, sales charges, and extraordinary expenses) in order to limit Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement for shares of the Fund's Class A Shares to 1.50% of the Fund's average net assets (the "Expense Cap"). The Expense Cap will remain in effect until at least July 31, 2014. This Expense Cap may not be changed or discontinued during the period without prior approval of the Board of Trustees. The agreement may be terminated at any time by the Board of Trustees upon written notice to the Investment Adviser and will terminate if the Management Agreement is terminated.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	RAINIER INVESTMENT MANAGEMENT MUTUAL FUNDS
Prospectus Date	rr_ProspectusDate	Nov. 30, 2012
Rainier International Discovery Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Rainier International Discovery Fund Class A Shares
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Rainier International Discovery Fund (the “International Discovery Fund” or “Fund”) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $25,000 in the Rainier Funds. More information about these and other discounts is available from your financial professional and in the section titled “Purchasing Shares” on page 15 of the Prospectus and “Additional Purchase and Redemption Information” on page B-37 of the Fund’s Statement of Additional Information.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
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	July 31, 2014
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	PORTFOLIO TURNOVER
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal period from March 28, 2012 through March 31, 2012, the Fund’s turnover rate was 0.23% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	0.23%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	If no initial sales charge was assessed in certain circumstances, such as on a purchase of $1 million or more, a contingent deferred sales charge of 1.00% of the lesser of the initial offering price of the shares redeemed or the amount redeemed within one year of purchase may be assessed.
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $25,000 in the Rainier Funds.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	25,000
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	Other Expenses are based on estimated amounts for the current fiscal year and include 0.31% for organizational costs which cover various one-time costs related to starting up the Fund.
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 shares of 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 redeem all of your 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 (taking into account the contractual expense limitation in the first year). Although your actual cost may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal conditions the Fund will invest primarily in equity securities of companies that are small- to medium-sized at the time of purchase and are located in foreign developed countries and emerging market countries and that have strong earnings prospects relative to their peers and attractive overall business fundamentals. The portfolio manager selects stocks of companies he believes will increase in value over time and makes investment decisions based primarily on an analysis of individual companies, rather than on broad economic forecasts. The portfolio manager believes that, over the long term, stock price movements follow growth in earnings, revenues and/or cash flow. In normal market conditions, the Fund’s portfolio will primarily consist of securities of companies whose earnings or revenues are not only growing, but growing at an accelerating pace. The Investment Adviser refers to its stock selection philosophy as Growth at a Reasonable Price (“GARP”). Stock selection focuses on companies that are likely to demonstrate superior earnings growth relative to their peers, and whose equities are selling at attractive relative valuations. In pursuing its investment objective, the Fund may invest in equity securities, including common stock and preferred stock, and securities convertible into common stock, including warrants, convertible bonds, and rights. In addition, the Fund may also invest in the initial public offerings (“IPOs”) of small-cap companies, real estate investment trusts (“REITs”) and similar types of investments outside of the U.S., and in certain derivatives including futures, options, forward contracts and participatory notes. Participatory notes allow investors, such as the Fund, to invest indirectly in foreign securities without registering in those foreign markets where the country requires registration to make any direct investment in securities. The Fund will generally not invest more than 25% of its net assets in participatory notes at the time of purchase. The Fund will invest primarily in foreign securities, including American Depositary Receipts (“ADRs”), Global Depositary Receipts (“GDRs”), International Depositary Receipts (“IDRs”), U.S. dollar-denominated foreign securities and direct foreign securities (purchased on foreign exchanges). An IDR is a negotiable, bank-issued certificate representing ownership of stock securities by an investor outside the country of origin. An IDR is the non-U.S. equivalent of an ADR. The Fund is not required to invest a specified portion of its net assets in any particular geographic region or any particular industry or sector, but will typically invest in at least three foreign countries at any time. The Fund will generally not invest more than 50% of its net assets in issuers located in emerging markets. The Fund is diversified and will generally hold between 60 and 120 securities and seeks to invest in securities that are selling at reasonable valuations. The Fund may sell a security, if it achieves the valuation target, or the underlying fundamentals deteriorate as compared to the portfolio manager’s expectations, or when it is replaced with a more attractive security. In addition, up to 10% of the Fund’s net assets may be held in cash or cash equivalents at the Investment Adviser’s discretion.
Risk [Heading]	rr_RiskHeading	PRINCIPAL INVESTMENT RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Because the Fund invests in securities that normally experience daily price changes, there is the risk that an investor could lose money. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. The following risks could affect the value of your investment: Foreign Securities and Emerging Markets Risks – Investing in foreign securities and securities of companies located in emerging market countries involve additional risks as compared to investing in U.S. securities, including risks related to currency- exchange rate fluctuations, political and economic instability, differences in financial reporting, accounting, auditing and legal standards, nationalization, expropriation or confiscatory taxation, less-strict regulation of securities markets, less liquidity, more volatility, higher transaction costs, and delays in settling securities transactions. Investing in securities of companies located in emerging market countries involves even greater risk and volatility than investing in more developed foreign markets because of, among other things, smaller securities markets, higher transaction costs, and fixed or managed currencies. Growth Stock Risk – Growth stocks may fall out of favor with investors. Because growth stocks can have relatively high valuations, an investment in a growth stock can be more risky than an investment in a company with more modest growth expectations. IPO Risk – IPO share prices can be volatile and fluctuate considerably due to factors such as the absence of a prior public market, unseasoned trading, a limited number of shares available for trading, and limited operating history and/or information about the issuer. The purchase of IPO shares may involve high transaction costs. IPO shares are subject to market risk and liquidity risk. When the Fund’s asset base is small, investment in IPO shares could have a magnified impact on the performance of the Fund. Market Risk – The securities markets could decline or companies represented in the Fund may weaken or otherwise not meet market expectations. The securities markets have been subject to significant volatility recently which has increased the risks associated with an investment in the Fund. Management Risk – Like all managed funds, there is risk that the Investment Adviser’s strategy for managing the Fund may not achieve the desired results or may be less effective than other strategies in a particular market environment. Government Sponsored Entities Risk – Securities issued or guaranteed by government-sponsored entities may not be guaranteed or insured by the United States Government, and may only be supported by the credit of the issuing agency. New Fund Risk – There can be no guarantee that the Fund will grow to or maintain an economically viable size. Participatory Notes Risk – Investments in participatory notes involve risks normally associated with a direct investment in the underlying securities. In addition, participatory notes are subject to counterparty risk, which is the risk that the broker-dealer or bank that issues the participatory notes will not fulfill its contractual obligation to complete the transaction with the Fund. Real Estate Securities Risk – The value of a REIT and similar U.S. and foreign investments can be negatively affected by economic downturns or by changes in real estate values, rents, property taxes, interest rates, tax treatment, regulations, or the legal structure of the entity. Small-Cap Company Risk – Investments in securities of small-cap companies involve greater risk of loss than investing in larger, more established companies. Small-cap companies may have limited product lines, markets or financial resources and less seasoned management teams and may trade less frequently and at a lower volume than more widely held securities. The prices of small-cap companies’ stock tend to fluctuate in value more than other stocks. Derivatives Risk – The prices of derivatives may move in unexpected ways due to the use of leverage and other factors and may result in increased volatility or losses. The Fund may not be able to terminate or sell derivative positions, and a liquid secondary market may not always exist for derivative positions. The use of derivatives may also involve the risk that a counterparty to a derivative contract will fail to comply with the terms of the contract which could cause the Fund to lose its investment in the derivative instrument.
Risk Lose Money [Text]	rr_RiskLoseMoney	Because the Fund invests in securities that normally experience daily price changes, there is the risk that an investor could lose money.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	Because the Fund does not have a full calendar year of performance to compare against a broad measure of market performance, performance information is not provided here. Performance information will be available after the Fund has been in operation for one calendar year. At that time, the performance information will provide some indication of the risks of investing in the Fund by comparing it against a broad measure of market performance.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	Because the Fund does not have a full calendar year of performance to compare against a broad measure of market performance, performance information is not provided here. Performance information will be available after the Fund has been in operation for one calendar year.
Rainier International Discovery Fund | Class A Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum Deferred Sales Charge (Load)	rr_MaximumDeferredSalesChargeOverOther	none	[1]
Maximum Sales Charge (Load) on Reinvested Dividends	rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther	none
Redemption or Exchange Fee	rr_RedemptionFeeOverRedemption	none
Management Fees	rr_ManagementFeesOverAssets	1.00%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	1.12%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.37%
Fee Reduction and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.87%)
Total Annual Fund Operating Expenses After Fee Reduction and/or Expense Reimbursement	rr_NetExpensesOverAssets	1.50%	[3]
1 Year	rr_ExpenseExampleYear01	719
3 Years	rr_ExpenseExampleYear03	1,133

[1] If no initial sales charge was assessed in certain circumstances, such as on a purchase of $1 million or more, a contingent deferred sales charge of 1.00% of the lesser of the initial offering price of the shares redeemed or the amount redeemed within one year of purchase may be assessed.

[2] Other Expenses are based on estimated amounts for the current fiscal year and include 0.31% for organizational costs which cover various one-time costs related to starting up the Fund.

[3] The Investment Adviser has contractually agreed to reduce its fees and/or pay Fund expenses (excluding Acquired Fund Fees and Expenses, interest, taxes, brokerage commissions, sales charges, and extraordinary expenses) in order to limit Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement for shares of the Fund's Class A Shares to 1.50% of the Fund's average net assets (the "Expense Cap"). The Expense Cap will remain in effect until at least July 31, 2014. This Expense Cap may not be changed or discontinued during the period without prior approval of the Board of Trustees. The agreement may be terminated at any time by the Board of Trustees upon written notice to the Investment Adviser and will terminate if the Management Agreement is terminated.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	RAINIER INVESTMENT MANAGEMENT MUTUAL FUNDS
Prospectus Date	rr_ProspectusDate	Nov. 30, 2012
Document Creation Date	dei_DocumentCreationDate	Nov. 30, 2012

XML

Document and Entity Information	12 Months Ended
	Nov. 30, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	Nov. 30, 2012
Registrant Name	RAINIER INVESTMENT MANAGEMENT MUTUAL FUNDS
Central Index Key	0000917125
Amendment Flag	false
Document Creation Date	Nov. 30, 2012
Document Effective Date	Nov. 30, 2012
Prospectus Date	Nov. 30, 2012