William Blair Funds

Prospectus

May 1, 2022

William Blair Funds


U.S. Equity Funds	Class N	Class I	Class R6
Growth Fund	WBGSX	BGFIX	BGFRX
Large Cap Growth Fund	LCGNX	LCGFX	LCGJX
Mid Cap Growth Fund	WCGNX	WCGIX	WCGJX
Mid Cap Value Fund	—	WVMIX	WVMRX
Small‑Mid Cap Core Fund	—	WBCIX	WBCRX
Small‑Mid Cap Growth Fund	WSMNX	WSMDX	WSMRX
Small Cap Growth Fund	WBSNX	WBSIX	WBSRX
Small Cap Value Fund	WBVNX	ICSCX	WBVRX

Global/International Funds	Class N	Class I	Class R6
Global Leaders Fund	WGGNX	WGFIX	BGGIX
International Leaders Fund	WILNX	WILIX	WILJX
International Growth Fund	WBIGX	BIGIX	WBIRX
Institutional International Growth Fund (WBIIX)	—	—	—
International Small Cap Growth Fund	WISNX	WISIX	WIISX
Emerging Markets Leaders Fund	WELNX	WBELX	WELIX
Emerging Markets Growth Fund	WBENX	WBEIX	BIEMX
Emerging Markets Small Cap Growth Fund	WESNX	BESIX	WESJX
China Growth Fund	—	WICGX	WRCGX

Emerging Markets Debt Fund	Class N	Class I	Class R6
Emerging Markets Debt Fund	—	WEDIX	WEDRX

The U.S. Securities and Exchange Commission has not approved or disapproved these securities or passed upon the accuracy or adequacy of this Prospectus. Any representation to the contrary is a criminal offense.

William Blair Funds

150 North Riverside Plaza

Chicago, Illinois 60606

TABLE OF CONTENTS


Summary			1

William Blair Growth Fund			1

William Blair Large Cap Growth Fund			6

William Blair Mid Cap Growth Fund			11

William Blair Mid Cap Value Fund			16

William Blair Small‑Mid Cap Core Fund			21

William Blair Small‑Mid Cap Growth Fund			26

William Blair Small Cap Growth Fund			31

William Blair Small Cap Value Fund			36

William Blair Global Leaders Fund			42

William Blair International Leaders Fund			48

William Blair International Growth Fund			54

William Blair Institutional International Growth Fund			59

William Blair International Small Cap Growth Fund			64

William Blair Emerging Markets Leaders Fund			69

William Blair Emerging Markets Growth Fund			75

William Blair Emerging Markets Small Cap Growth Fund			81

William Blair China Growth Fund			87

William Blair Emerging Markets Debt Fund			93

Additional Information Regarding Investment Objectives and Strategies			101

Principal Risks			104

Management of the Funds			119

Your Account			128

Class N Shares			128

Class I Shares			128

Class R6 Shares			129

Additional Information and Exceptions to Eligibility and Minimum Investment Requirements for Class N, Class I and Class R6 Shares			130

Additional Information for Class N Shares			130

Additional Information on Other Payments to Financial Intermediaries			131

International Growth Fund, Institutional International Growth Fund, International Small Cap Growth Fund and Emerging Markets Small Cap Growth Fund			131

Buying, Selling and Exchanging Shares			132

How to Buy Shares			132

How to Sell Shares			135

How to Exchange Shares			137

Dividends and Distributions			138

Federal Income Taxes			139

Shareholder Services and Account Policies			141

Determination of Net Asset Value			144

Investment Glossary			146

Financial Highlights			151

For More Information			181

WILLIAM BLAIR GROWTH FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.

Shareholder Fees (fees paid directly from your investment):

Class N

Class I

Class R6

Maximum Sales Charge (Load) Imposed on Purchases

None

Redemption Fee

None

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


	Class N		Class I		Class R6
Management Fee		0.75%		0.75%		0.75%
Distribution (Rule 12b‑1) Fee		0.25%		None		None
Other Expenses		0.21%		0.14%		0.09%

Total Annual Fund Operating Expenses		1.21%		0.89%		0.84%
Fee Waiver and/or Expense Reimbursement*		0.01%		N/A		N/A

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		1.20%		0.89%		0.84%

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 the Fund’s operating expenses remain the same. The figures reflect the expense limitation for the first year. 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 N		$122		$383		$664		$1,465
Class I		91		284		493		1,096
Class R6		86		268		466		1,037

operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 30% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES: The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of domestic growth companies of all sizes that are expected to exhibit quality growth characteristics. The Fund invests primarily in equity securities issued by companies that typically have market capitalizations no smaller than the smallest capitalized company, and no larger than the largest capitalized company, included in the Russell 3000^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to companies in the Russell 3000^® Index, but that may have market capitalizations outside the range of companies included in the index.

The Russell 3000^® Index is a widely recognized, unmanaged index that measures the performance of the 3,000 largest U.S. companies. The size of companies in the Russell 3000^® Index may change with market conditions. In addition, changes to the composition of the Russell 3000^® Index can change the market capitalization range of the companies in the index. As of March 31, 2022, the Russell 3000^® Index included securities issued by companies that ranged in size between $21.6 million and $2.8 trillion. The Russell 3000^® Growth Index, the Fund’s benchmark, measures the performance of Russell 3000^® companies with higher price‑to‑book ratios and higher forecasted growth values.

In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be, or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (for example, this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of U.S. growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Market Risk. The value of the Fund’s investments may go up or down, sometimes rapidly or unpredictably. The value of an investment may decline due to factors affecting securities markets generally or particular industries represented in the securities markets. The value of an investment may decline due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic conditions, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. Events such as war, acts of terrorism, social unrest, natural disasters, the spread of infectious illness or other public health threats could also significantly impact the Fund and its investments. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general

downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.

Smaller Company Risk. Stocks of smaller companies involve greater risk than those of larger, more established companies. This is because smaller companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of smaller companies may be more volatile and less liquid than securities of large capitalized companies.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the growth investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

Operational and Technology Risk. Cyber-attacks, disruptions, or failures that affect the Fund’s service providers, counterparties, market participants, or issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.


		Highest Quarterly Return 25.68% (2Q20)		Lowest Quarterly Return (14.33)% (4Q18)

Average Annual Total Returns (For the periods ended December 31, 2021). The table below shows returns on a before‑tax and after‑tax basis for Class N shares and on a before‑tax basis for Class I and Class R6 shares. After‑tax returns for Class I and Class R6 shares will vary. After‑tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after‑tax returns depend on an investor’s tax situation and may differ from those shown. After‑tax returns are not relevant to investors who hold their Fund shares through tax‑deferred arrangements, such as 401(k) plans or individual retirement accounts.


	1 Year		5 Years		10 Years
Class N Shares
Return Before Taxes		22.09%		23.42%		17.39%
Return After Taxes on Distributions		17.96%		18.01%		13.51%
Return After Taxes on Distributions and Sale of Fund Shares		15.41%		17.43%		13.22%

Class I Shares
Return Before Taxes		22.54%		23.77%		17.75%

Russell 3000^® Growth Index (reflects no deduction for fees, expenses or taxes)		25.85%		24.56%		19.39%
S&P 500^® Index (reflects no deduction for fees, expenses or taxes)		28.71%		18.47%		16.55%


	1 Year		Since Share Class Inception (May 2, 2019)
Class R6 Shares
Return Before Taxes		22.55%		25.99%

Russell 3000^® Growth Index (reflects no deduction for fees, expenses or taxes)		25.85%		28.71%
S&P 500^® Index (reflects no deduction for fees, expenses or taxes)		28.71%		22.17%

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). David Fording, a Partner of the Adviser, manages the Fund. Mr. Fording has managed or co‑managed the Fund since 2006.

PURCHASE AND SALE OF FUND SHARES:

Class N Share Purchase. The minimum initial investment for an account generally is $2,500. The minimum subsequent investment generally is $1,000. Certain exceptions to the minimum initial and subsequent investment amounts may apply. See “Your Account—Class N Shares” for additional information on eligibility requirements applicable to purchasing Class N shares.

investment for qualified retirement plans, including, but not limited to, 401(k) plans, 457 plans, employer- sponsored 403(b) plans, defined benefit plans and other similar accounts, or plans whereby Class I shares are held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. William Blair may make certain additional exceptions to the minimum initial investment amount in its discretion. Class I shares are only available to certain investors. See “Your Account—Class I Shares” for additional information on the eligibility requirements and investment minimums applicable to purchasing Class I shares.

Class R6 Share Purchase. The minimum initial investment for an account is $1 million (or any lesser amount if, in William Blair’s opinion, the investor has adequate intent and availability of funds to reach a future level of investment of $1 million). There is no minimum for subsequent purchases. There is no minimum initial investment for qualified retirement plans, including, but not limited to, 401(k) plans, 457 plans, employer-sponsored 403(b) plans, defined benefit plans and other similar accounts, or plans whereby Class R6 shares are held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. William Blair may make certain additional exceptions to the minimum initial investment amount in its discretion. Class R6 shares are only available to certain investors. See “Your Account—Class R6 Shares” for additional information on eligibility requirements and investment minimums applicable to purchasing Class R6 shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

TAX INFORMATION: The Fund intends to make distributions that may be taxed as ordinary income or capital gains, unless you are investing through a tax‑advantaged investment plan. If you are investing through a tax‑advantaged investment plan, withdrawals from the tax‑advantaged investment plan may be subject to taxes.

PAYMENTS TO BROKER-DEALERS AND OTHER FINANCIAL INTERMEDIARIES: If you purchase shares of the Fund through a broker-dealer or other financial intermediary (such as a bank), the Fund and its related companies may pay the intermediary for the sale of shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary’s website for more information.

WILLIAM BLAIR LARGE CAP GROWTH FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair Large Cap Growth Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):

Class N

Class I

Class R6

Maximum Sales Charge (Load) Imposed on Purchases

None

Redemption Fee

None

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


	Class N		Class I		Class R6
Management Fee		0.60%		0.60%		0.60%
Distribution (Rule 12b‑1) Fee		0.25%		None		None
Other Expenses		0.20%		0.15%		0.07%

Total Annual Fund Operating Expenses		1.05%		0.75%		0.67%
Fee Waiver and/or Expense Reimbursement*		0.15%		0.10%		0.07%

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		0.90%		0.65%		0.60%


	1 Year		3 Years		5 Years		10 Years
Class N		$92		$319		$565		$1,269
Class I		66		230		407		921
Class R6		61		207		366		828

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 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 year, the Fund’s portfolio turnover rate was 26% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of large capitalized (“large cap”) companies. The Fund invests primarily in a portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of large cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Adviser considers a company to be a large cap company if it has a market capitalization no smaller than the smallest capitalized company included in the Russell 1000^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to large cap companies, but that may have market capitalizations below the market capitalization of the smallest member of the Russell 1000^® Index.

The Russell 1000^® Index is a widely recognized, unmanaged index that measures the performance of the 1,000 largest U.S. companies. The companies in the Russell 1000^® Index are considered representative of large cap companies. The size of companies in the Russell 1000^® Index may change with market conditions. In addition, changes to the composition of the Russell 1000^® Index can change the market capitalization range of the companies included in the index. As of March 31, 2022, the Russell 1000^® Index included securities issued by companies that ranged in size between $364.7 million and $2.8 trillion. The Russell 1000^® Growth Index, the Fund’s benchmark, measures the performance of those Russell 1000 companies with a greater-than-average growth orientation.

THE FUND IS NON‑DIVERSIFIED UNDER THE INVESTMENT COMPANY ACT OF 1940, AS AMENDED, AND MAY INVEST A LARGER PERCENTAGE OF ITS ASSETS IN FEWER ISSUERS THAN DIVERSIFIED MUTUAL FUNDS.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of large cap U.S. growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Non‑Diversification Risk. The Fund is non‑diversified, meaning that it is permitted to invest a larger percentage of its assets in fewer issuers than diversified mutual funds. Thus, the Fund may be more susceptible to adverse developments affecting any single issuer held in its portfolio, and may be more susceptible to greater losses because of these developments.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.


		Highest Quarterly Return 25.58% (2Q20)		Lowest Quarterly Return (12.70)% (1Q20)


	1 Year		5 Years		10 Years
Class N Shares
Return Before Taxes		28.03%		26.66%		20.40%
Return After Taxes on Distributions		26.66%		24.86%		18.57%
Return After Taxes on Distributions and Sale of Fund Shares		17.53%		21.52%		16.69%

Class I Shares
Return Before Taxes		28.39%		27.00%		20.72%

Russell 1000^® Growth Index (reflects no deduction for fees, expenses or taxes)		27.60%		25.32%		19.79%


	1 Year		Since Share Class Inception (May 2, 2019)
Class R6 Shares
Return Before Taxes		28.42%		29.75%

Russell 1000^® Growth Index (reflects no deduction for fees, expenses or taxes)		27.60%		29.63%

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). James Golan, a Partner of the Adviser, and David Ricci, a Partner of the Adviser, co‑manage the Fund. Mr. Golan has co‑managed the Fund since 2005. Mr. Ricci has co‑managed the Fund since 2011.

PURCHASE AND SALE OF FUND SHARES:

Class I Share Purchase. The minimum initial investment for an account generally is $500,000 (or any lesser amount if, in William Blair’s opinion, the investor has adequate intent and availability of funds to reach a future level of investment of $500,000). There is no minimum for subsequent purchases. There is no minimum initial investment for qualified retirement plans, including, but not limited to, 401(k) plans, 457 plans, employer-sponsored 403(b) plans, defined benefit plans and other similar accounts, or plans whereby Class I shares are held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. William Blair may make certain additional exceptions to the minimum initial investment amount in its discretion. Class I shares are only available to certain investors. See “Your Account—Class I Shares” for additional information on the eligibility requirements and investment minimums applicable to purchasing Class I shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

WILLIAM BLAIR MID CAP GROWTH FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair Mid Cap Growth Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):

Class N

Class I

Class R6

Maximum Sales Charge (Load) Imposed on Purchases

None

Redemption Fee

None

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


	Class N		Class I		Class R6
Management Fee		0.90%		0.90%		0.90%
Distribution (Rule 12b‑1) Fee		0.25%		None		None
Other Expenses		0.33%		0.34%		0.21%

Total Annual Fund Operating Expenses		1.48%		1.24%		1.11%
Fee Waiver and/or Expense Reimbursement*		0.28%		0.29%		0.21%

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		1.20%		0.95%		0.90%


	1 Year		3 Years		5 Years		10 Years
Class N		$122		$440		$781		$1,744
Class I		97		365		653		1,474
Class R6		92		332		591		1,333

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of medium capitalized (“mid cap”) companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of mid cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Adviser considers a company to be a mid cap company if it has a market capitalization no smaller than the smallest capitalized company, and no larger than the largest capitalized company, included in the Russell Midcap^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to mid cap companies, but that may have market capitalizations above the market capitalization of the largest member, or below the market capitalization of the smallest member, of the Russell Midcap^® Index.

The Russell Midcap^® Index measures the performance of the 800 companies with the lowest market capitalizations in the Russell 1000^® Index. The companies in the Russell Midcap^® Index are considered representative of mid cap companies. The size of companies in the Russell Midcap^® Index may change with market conditions. In addition, changes to the composition of the Russell Midcap^® Index can change the market capitalization range of companies included in the index. As of March 31, 2022, the Russell Midcap^® Index included securities issued by companies that ranged in size between $364.7 million and $61.3 billion. The Russell Midcap^® Growth Index, the Fund’s benchmark, measures the performance of the smallest 800 companies in the Russell 1000^® Index with a greater-than-average growth orientation.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of mid cap U.S. growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

conditions that are not specifically related to a particular company, such as real or perceived adverse economic conditions, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. Events such as war, acts of terrorism, social unrest, natural disasters, the spread of infectious illness or other public health threats could also significantly impact the Fund and its investments. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.

Mid Cap Company Risk. Stocks of mid cap companies involve greater risk than those of larger, more established companies. This is because mid cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of mid cap companies may be more volatile and less liquid than securities of large capitalized companies.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the years since the Fund started for Class N shares.


		Highest Quarterly Return 23.18% (2Q20)		Lowest Quarterly Return (19.93)% (1Q20)


	1 Year		5 Years		10 Years
Class N Shares
Return Before Taxes		8.10%		17.36%		13.09%
Return After Taxes on Distributions		6.69%		14.25%		10.31%
Return After Taxes on Distributions and Sale of Fund Shares		5.35%		13.17%		9.94%

Class I Shares
Return Before Taxes		8.38%		17.66%		13.38%

Russell Midcap^® Growth Index (reflects no deduction for fees, expenses or taxes)		12.73%		19.83%		16.63%


	1 Year		Since Share Class Inception (May 2, 2019)
Class R6 Shares
Return Before Taxes		8.44%		16.55%

Russell Midcap^® Growth Index (reflects no deduction for fees, expenses or taxes)		12.73%		21.30%

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Daniel Crowe, a Partner of the Adviser, and James Jones, a Partner of the Adviser, co‑manage the Fund. Mr. Crowe has co‑managed the Fund since 2015. Mr. Jones has co‑managed the Fund since 2019.

PURCHASE AND SALE OF FUND SHARES:

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

WILLIAM BLAIR MID CAP VALUE FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair Mid Cap Value Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):


	Class I		Class R6
Maximum Sales Charge (Load) Imposed on Purchases		None		None
Redemption Fee		None		None

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


	Class I		Class R6
Management Fee		0.70%		0.70%
Distribution (Rule 12b‑1) Fee		None		None
Other Expenses*		0.41%		0.30%

Total Annual Fund Operating Expenses		1.11%		1.00%
Fee Waiver and/or Expense Reimbursement**		0.36%		0.30%

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		0.75%		0.70%

*	Other Expenses are based on estimated amounts for the current fiscal period.

William Blair Investment Management, LLC (the “Adviser”) has entered into a contractual agreement with the Fund to waive fees and/or reimburse expenses in order to limit the Fund’s operating expenses (excluding interest expenses, taxes, brokerage commissions, acquired fund fees and expenses, dividend and interest expenses on short sales, other investment-related costs and extraordinary expenses, such as litigation and other expenses not incurred in the ordinary course of the Fund’s business) to 0.75% and 0.70% of average daily net assets for Class I and Class R6 shares, respectively, until April 30, 2024. The Adviser may not terminate this contractual agreement prior to April 30, 2024 without the approval of the Fund’s Board of Trustees. The Adviser is entitled to recoupment of previously waived fees and reimbursed expenses for a period of three years subsequent to the Fund’s commencement of operations to the extent that such recoupment does not cause the annual Fund operating expenses (after the recoupment is taken into account) to exceed both (1) the expense limit in place when such amounts were waived or reimbursed and (2) the Fund’s current expense limitation.

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 the Fund’s operating expenses remain the same. The figures reflect the expense limitation for the first two years. Although your actual costs may be higher or lower, based on these assumptions your costs would be:


	1 Year		3 Years
Class I		$77		$279
Class R6		72		257

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 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. Because the Fund had not commenced operations as of December 31, 2021, no portfolio turnover rate information is available.

PRINCIPAL INVESTMENT STRATEGIES: Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of medium capitalized (“mid cap”) companies. For purposes of the Fund, the Adviser considers a company to be a mid cap company if it has a market capitalization no smaller than the smallest capitalized company, and no larger than the largest capitalized company, included in the Russell Midcap^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and value prospects similar to mid cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell Midcap^® Index. The Fund may invest in equity securities listed on a national securities exchange or traded in the over‑the‑counter markets. The Fund invests primarily in common stocks, but it may also invest in other types of equity securities, including real estate investment trusts (“REITs”) and American Depositary Receipts (“ADRs”).

The Russell Midcap^® Index measures the performance of the mid‑cap segment of the U.S. equity universe. The Russell Midcap^® Index is a subset of the Russell 1000^® Index. It includes approximately 800 of the smallest securities based on a combination of their market cap and current index membership. The Russell Midcap^® Index represents approximately 26% of the total market capitalization of the Russell 1000^® companies as of March 31, 2022. The companies in the Russell Midcap^® Index are considered representative of mid cap companies. The size of companies in the Russell Midcap^® Index may change with market conditions. In addition, changes to the composition of the Russell Midcap^® Index can change the market capitalization range of the companies included in the index. As of March 31, 2022, the Russell Midcap^® Index included securities issued by companies that ranged in size between $364.7 million and $61.3 billion. The Russell Midcap^® Value Index, the Fund’s benchmark, measures the performance of those Russell Midcap companies with lower price‑to‑book ratios and lower forecasted growth values.

In selecting investments for the Fund, the Adviser typically looks to invest in companies with leading market share positions, shareholder oriented managements, and strong balance sheet and cash flow ratios. Usually, the shares of the companies the Adviser buys are selling at a price to earnings ratio below the average price to earnings ratio of the stocks that comprise the Russell Midcap^® Index. In addition, the companies selected by the Adviser usually have higher returns on equity and capital than the average company in the Russell Midcap^® Index. The Adviser screens the Fund’s universe of potential investments to identify potentially undervalued securities based on factors such as financial strength, earnings valuation, and earnings quality. The Adviser further narrows the list of potential investments through traditional fundamental security analysis, which may include interviews with company management and a review of the assessments and opinions of outside analysts and consultants. Securities are sold when the Adviser believes the shares have become relatively overvalued or it finds more attractive alternatives. The Adviser generally will not sell a security merely due to market appreciation outside the Fund’s target capitalization range if it believes the company has growth potential.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

The principal risks of investing in the Fund are:

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of U.S. mid cap value companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

REIT Risk. REITs are pooled investment vehicles that own, and usually operate, income-producing real estate. REITs are susceptible to the risks associated with direct ownership of real estate, such as the following: declines in property values; increases in property taxes, operating expenses, interest rates or competition; overbuilding; zoning changes; and losses from casualty or condemnation. REITs typically incur fees that are separate from those of the Fund. Accordingly, the Fund’s shareholders will indirectly bear a proportionate share of the REITs’ operating expenses, in addition to paying Fund expenses. REIT operating expenses are not reflected in the fee table and example in this Prospectus.

Foreign Securities Risk. The Fund’s investments in ADRs are subject to foreign securities risk. ADRs are certificates evidencing ownership of shares of a foreign issuer that are issued by depositary banks and traded on U.S. exchanges. Although ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies, they continue to be subject to many of the risks associated with investing directly in foreign securities.

New Fund Risk. As a new fund, there can be no assurance that the Fund will grow to or maintain an economically viable size, in which case it could ultimately liquidate.

Share Ownership Concentration Risk. To the extent that a significant portion of the Fund’s shares is held by a limited number of shareholders or their affiliates, there is a risk that the share trading activities of these shareholders could disrupt the Fund’s investment strategies, which could have adverse consequences for the Fund and other shareholders (e.g., by requiring the Fund to sell investments at inopportune times or causing the Fund to maintain larger-than-expected cash positions pending acquisition of investments). In addition, separate accounts managed by the Adviser may invest in the Fund and, therefore, the Adviser at times may have discretionary authority over a significant portion of the assets of the Fund. In such instances, the Adviser’s decision to make changes to or rebalance its clients’ allocations in the separate accounts may substantially impact the Fund’s performance.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the value investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

FUND PERFORMANCE HISTORY: Information on the Fund’s annual total returns and average annual total returns will be provided after the Fund has completed a full calendar year of operations. Updated performance information will be available on the Fund’s website at www.williamblairfunds.com or by calling 1‑800‑635‑2886.

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Matthew Fleming, CFA, an Associate of the Adviser, and William V. Heaphy, CFA, an Associate of the Adviser, co‑manage the Fund. Mr. Fleming and Mr. Heaphy have each co‑managed the Fund since its inception in 2022.

PURCHASE AND SALE OF FUND SHARES:

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

WILLIAM BLAIR SMALL‑MID CAP CORE FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair Small‑Mid Cap Core Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):


	Class I		Class R6
Maximum Sales Charge (Load) Imposed on Purchases		None		None
Redemption Fee		None		None

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


	Class I		Class R6
Management Fee		0.90%		0.90%
Distribution (Rule 12b‑1) Fee		None		None
Other Expenses		0.35%		0.26%

Total Annual Fund Operating Expenses		1.25%		1.16%
Fee Waiver and/or Expense Reimbursement*		0.30%		0.26%

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		0.95%		0.90%

William Blair Investment Management, LLC (the “Adviser”) has entered into a contractual agreement with the Fund to waive fees and/or reimburse expenses in order to limit the Fund’s operating expenses (excluding interest expenses, taxes, brokerage commissions, acquired fund fees and expenses, dividend and interest expenses on short sales, other investment-related costs and extraordinary expenses, such as litigation and other expenses not incurred in the ordinary course of the Fund’s business) to 0.95% and 0.90% of average daily net assets for Class I and Class R6 shares, respectively, until April 30, 2023. The Adviser may not terminate this arrangement prior to April 30, 2023 without the approval of the Fund’s Board of Trustees. The Adviser is entitled to recoupment of previously waived fees and reimbursed expenses for a period of three years subsequent to the Fund’s commencement of operations to the extent that such recoupment does not cause the annual Fund operating expenses (after the recoupment is taken into account) to exceed both (1) the expense limit in place when such amounts were waived or reimbursed and (2) the Fund’s current expense limitation.


	1 Year		3 Years		5 Years		10 Years
Class I		$97		$367		$657		$1,485
Class R6		92		343		613		1,386

PRINCIPAL INVESTMENT STRATEGIES: Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalized (“small cap”) and medium capitalized (“mid cap”) companies. The Fund invests in a diversified portfolio of equity securities, primarily common stocks, of small cap and mid cap U.S. companies that the Adviser deems to be of high quality but undervalued by the marketplace. For purposes of the Fund, the Adviser considers a company to be a small cap or a mid cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell Midcap^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics similar to small cap and mid cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell Midcap^® Index.

The Russell Midcap^® Index measures the performance of the 800 companies with the lowest market capitalizations in the Russell 1000^® Index. The size of companies in the Russell Midcap^® Index may change with market conditions. In addition, changes to the composition of the Russell Midcap^® Index can change the market capitalization range of companies included in the index. As of March 31, 2022, the Russell Midcap^® Index included securities issued by companies that ranged in size between $364.7 million and $61.3 billion. The Russell 2500^TM Index, the Fund’s benchmark, measures the performance of the 2,500 smallest companies in the Russell 3000^® Index with a weighted average market capitalization of approximately $7.9 billion, median capitalization of $1.6 billion and market capitalization of the largest company at $39.3 billion as of March 31, 2022.

In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser evaluates the extent to which a company meets the criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be, or should have the expectation of becoming, a significant provider in the primary markets it serves; (b) the company should have some distinctive attribute relative to present or potential competitors (this may, for example, take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition); and (c) the company should have a strong management team.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of small cap and mid cap U.S. companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

investor sentiment generally. Events such as war, acts of terrorism, social unrest, natural disasters, the spread of infectious illness or other public health threats could also significantly impact the Fund and its investments. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.

Small and Mid Cap Company Risk. Stocks of small and mid cap companies involve greater risk than those of larger, more established companies. This is because small and mid cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Small and mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of small and mid cap companies may be more volatile and less liquid than securities of large capitalized companies.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

The Fund is not intended to be a complete investment program and is designed for long-term investors.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the calendar years since the Fund started for Class I shares.


		Highest Quarterly Return 28.67% (4Q20)		Lowest Quarterly Return (26.97)% (1Q20)

Average Annual Total Returns (For the periods ended December 31, 2021). The table below shows returns on a before‑tax and after‑tax basis for Class I shares and on a before‑tax basis for Class R6 shares. After‑tax returns for Class R6 shares will vary. After‑tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after‑tax returns depend on an investor’s tax situation and may differ from those shown. After‑tax returns are not relevant to investors who hold their Fund shares through tax‑deferred arrangements, such as 401(k) plans or individual retirement accounts.


	1 Year		Since Fund Inception (October 1, 2019)
Class I Shares
Return Before Taxes		26.63%		24.30%
Return After Taxes on Distributions		26.63%		24.29%
Return After Taxes on Distributions and Sale of Fund Shares		15.77%		19.07%

Class R6 Shares
Return Before Taxes		26.71%		24.34%

Russell 2500^TM Index (reflects no deduction for fees, expenses or taxes)		18.18%		21.08%

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Daniel Crowe, a Partner of the Adviser, and Ward Sexton, a Partner of the Adviser, co‑manage the Fund. Messrs. Crowe and Sexton have co‑managed the Fund since its inception in 2019.

PURCHASE AND SALE OF FUND SHARES:

held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. William Blair may make certain additional exceptions to the minimum initial investment amount in its discretion. Class I shares are only available to certain investors. See “Your Account—Class I Shares” for additional information on the eligibility requirements and investment minimums applicable to purchasing Class I shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

WILLIAM BLAIR SMALL‑MID CAP GROWTH FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair Small‑Mid Cap Growth Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):

Class N

Class I

Class R6

Maximum Sales Charge (Load) Imposed on Purchases

None

Redemption Fee

None

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


	Class N		Class I		Class R6
Management Fee		1.00%		1.00%		1.00%
Distribution (Rule 12b‑1) Fee		0.25%		None		None
Other Expenses		0.18%		0.16%		0.03%

Total Annual Fund Operating Expenses		1.43%		1.16%		1.03%
Fee Waiver and/or Expense Reimbursement*		0.08%		0.06%		N/A

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		1.35%		1.10%		1.03%


	1 Year		3 Years		5 Years		10 Years
Class N		$137		$445		$774		$1,706
Class I		112		363		633		1,404
Class R6		105		328		569		1,259

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small capitalized (“small cap”) and medium capitalized (“mid cap”) companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap and mid cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Adviser considers a company to be a small cap or mid cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell Midcap^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to small cap and mid cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell Midcap^® Index.

The Russell Midcap^® Index measures the performance of the 800 companies with the lowest market capitalizations in the Russell 1000^® Index. The size of companies in the Russell Midcap^® Index may change with market conditions. In addition, changes to the composition of the Russell Midcap^® Index can change the market capitalization range of companies included in the index. As of March 31, 2022, the Russell Midcap^® Index included securities issued by companies that ranged in size between $364.7 million and $61.3 billion. The Russell 2500^TM Growth Index, the Fund’s benchmark, measures the performance of those Russell 2500^TM companies with higher price‑to‑book ratios and higher forecasted growth values. The Russell 2500^TM Index measures the performance of the 2,500 smallest companies in the Russell 3000^® Index with a weighted average market capitalization of approximately $7.9 billion, median capitalization of $1.6 billion and market capitalization of the largest company at $ 39.3 billion as of March 31, 2022.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of small cap and mid cap U.S. growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

industries represented in the securities markets. The value of an investment may decline due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic conditions, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. Events such as war, acts of terrorism, social unrest, natural disasters, the spread of infectious illness or other public health threats could also significantly impact the Fund and its investments. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.


		Highest Quarterly Return 26.45% (2Q20)		Lowest Quarterly Return (20.39)% (1Q20)


	1 Year		5 Years		10 Years
Class N Shares
Return Before Taxes		8.27%		18.56%		16.18%
Return After Taxes on Distributions		5.53%		16.68%		14.57%
Return After Taxes on Distributions and Sale of Fund Shares		6.22%		14.62%		13.17%

Class I Shares
Return Before Taxes		8.56%		18.86%		16.46%

Russell 2500^TM Growth Index (reflects no deduction for fees, expenses or taxes)		5.04%		17.65%		15.75%


	1 Year		Since Share Class Inception (May 2, 2019)
Class R6 Shares
Return Before Taxes		8.60%		18.02%

Russell 2500^TM Growth Index (reflects no deduction for fees, expenses or taxes)		5.04%		19.46%

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

PURCHASE AND SALE OF FUND SHARES:

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

WILLIAM BLAIR SMALL CAP GROWTH FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair Small Cap Growth Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):

Class N

Class I

Class R6

Maximum Sales Charge (Load) Imposed on Purchases

None

Redemption Fee

None

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


	Class N		Class I		Class R6
Management Fee		1.10%		1.10%		1.10%
Distribution (Rule 12b‑1) Fee		0.25%		None		None
Other Expenses		0.21%		0.15%		0.06%

Total Annual Fund Operating Expenses		1.56%		1.25%		1.16%
Fee Waiver and/or Expense Reimbursement*		0.06%		N/A		N/A

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		1.50%		1.25%		1.16%


	1 Year		3 Years		5 Years		10 Years
Class N		$153		$487		$844		$1,851
Class I		127		397		686		1,511
Class R6		118		368		638		1,409

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small capitalized (“small cap”) companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap domestic growth companies that are expected to exhibit quality growth characteristics. The Fund’s investments in small cap companies may include a significant weighting to micro‑cap companies (which, for purposes of the Fund, are companies with market capitalizations of $1 billion or less at the time of the Fund’s investment). For purposes of the Fund, the Adviser considers a company to be a small cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell 2000^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to small cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell 2000^® Index.

The Russell 2000^® Index is a widely recognized, unmanaged index of common stocks that measures the performance of the 2,000 smallest companies in the Russell 3000^® Index. The companies in the Russell 2000^® Index are considered representative of small cap companies. The size of companies in the Russell 2000^® Index may change with market conditions. In addition, changes to the composition of the Russell 2000^® Index can change the market capitalization range of the companies included in the index. As of March 31, 2022, the Russell 2000^® Index included securities issued by companies that ranged in size between $21.6 million and $14.2 billion. The Russell 2000^® Growth Index, the Fund’s benchmark, measures the performance of those Russell 2000 companies with a greater-than-average growth orientation.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of small cap U.S. growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Small and Micro Cap Company Risk. Stocks of small and micro cap companies involve greater risk than those of larger, more established companies. This is because small and micro cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Small and micro cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of small and micro cap companies may be more volatile and less liquid than securities of large capitalized companies. For purposes of the Fund, micro cap companies are companies with market capitalizations of $1 billion or less at the time of the Fund’s investment.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.


		Highest Quarterly Return 29.72% (4Q20)		Lowest Quarterly Return (25.08)% (1Q20)


	1 Year		5 Years		10 Years
Class N Shares
Return Before Taxes		12.91%		18.81%		17.42%
Return After Taxes on Distributions		7.18%		15.12%		13.74%
Return After Taxes on Distributions and Sale of Fund Shares		9.95%		14.17%		13.08%

Class I Shares
Return Before Taxes		13.22%		19.11%		17.71%

Russell 2000^® Growth Index (reflects no deduction for fees, expenses or taxes)		2.83%		14.53%		14.14%


	1 Year		Since Share Class Inception (May 2, 2019)
Class R6 Shares
Return Before Taxes		13.31%		19.69%

Russell 2000^® Growth Index (reflects no deduction for fees, expenses or taxes)		2.83%		16.08%

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Ward Sexton, a Partner of the Adviser, and Mark Thompson, a Partner of the Adviser, co‑manage the Fund. Mr. Sexton has co‑managed the Fund since 2016. Mr. Thompson has co‑managed the Fund since 2020.

PURCHASE AND SALE OF FUND SHARES:

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

WILLIAM BLAIR SMALL CAP VALUE FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair Small Cap Value Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):

Class N

Class I

Class R6

Maximum Sales Charge (Load) Imposed on Purchases

None

Redemption Fee

None

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


	Class N		Class I		Class R6
Management Fee		0.75%		0.75%		0.75%
Distribution (Rule 12b‑1) Fee		0.25%		None		None
Other Expenses		0.26%		0.07%		0.03%

Total Annual Fund Operating Expenses		1.26%		0.82%		0.78%
Fee Waiver and/or Expense Reimbursement*		0.11%		N/A		N/A

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		1.15%		0.82%		0.78%


	1 Year		3 Years		5 Years		10 Years
Class N		$117		$389		$681		$1,513
Class I		84		262		455		1,014
Class R6		80		249		433		966

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 fiscal year ended October 31, 2021, the Fund’s portfolio turnover rate was 35% of the average value of its portfolio. During the two months ended December 31, 2021, the Fund’s portfolio turnover rate was 7% of the average value of its portfolio. The portfolio turnover rates reflect both that of the ICM Small Company Portfolio (the “Predecessor Fund”) prior to July 16, 2021, the date the Fund acquired the assets and assumed the liabilities of the Predecessor Fund in a reorganization (the “Reorganization”) and the portfolio turnover of the Fund subsequent to such date.

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalized (“small cap”) companies. For purposes of the Fund, the Adviser considers a company to be a small cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell 2000^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and value prospects similar to small cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell 2000^® Index. The Fund may invest in equity securities listed on a national securities exchange or traded in the over‑the‑counter markets. The Fund invests primarily in common stocks, but it may also invest in other types of equity securities, including real estate investment trusts (“REITs”) and American Depositary Receipts (“ADRs”).

The Russell 2000^® Index is a widely recognized, unmanaged index of common stocks that measures the performance of the 2,000 smallest companies in the Russell 3000^® Index. The companies in the Russell 2000^® Index are considered representative of small cap companies. The size of companies in the Russell 2000^® Index may change with market conditions. In addition, changes to the composition of the Russell 2000^® Index can change the market capitalization range of the companies included in the index. As of March 31, 2022, the Russell 2000^® Index included securities issued by companies that ranged in size between $21.6 million and $14.2 billion. The Russell 2000^® Value Index, the Fund’s benchmark, measures the performance of those Russell 2000 companies with lower price‑to‑book ratios and lower forecasted growth values.

In selecting investments for the Fund, the Adviser typically looks to invest in companies with leading market share positions, shareholder oriented managements, and strong balance sheet and cash flow ratios. Usually, the shares of the companies the Adviser buys are selling at a price to earnings ratio below the average price to earnings ratio of the stocks that comprise the Russell 2000^® Index. In addition, the companies selected by the Adviser usually have higher returns on equity and capital than the average company in the Russell 2000^® Index. The Adviser screens the Fund’s universe of potential investments to identify potentially undervalued securities based on factors such as financial strength, earnings valuation, and earnings quality. The Adviser further narrows the list of potential investments through traditional fundamental security analysis, which may include interviews with company management and a review of the assessments and opinions of outside analysts and consultants. Securities are sold when the Adviser believes the shares have become relatively overvalued or it finds more attractive alternatives. The Adviser generally will not sell a security merely due to market appreciation outside the Fund’s target capitalization range if it believes the company has growth potential.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of U.S. small cap value companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Small and Micro Cap Company Risk. Stocks of small and micro cap companies involve greater risk than those of larger, more established companies. This is because small and micro cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Small and micro cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of small and micro cap companies may be more volatile and less liquid than securities of large capitalized companies. For purposes of the Fund, micro cap companies are companies with market capitalizations of $500 million or less at the time of the Fund’s investment.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the value investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

Portfolio Turnover Rate Risk. Higher portfolio turnover rates involve correspondingly higher transaction costs, which are borne directly by the Fund. In addition, the Fund may realize significant short-term and long-term capital gains if portfolio turnover rate is high, which will result in taxable distributions to investors that may be greater than those made by other funds with lower portfolio turnover rates.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. On July 16, 2021, the Fund acquired the assets and assumed the liabilities of the Predecessor Fund, a series of The Advisors’ Inner Circle Fund. In the Reorganization, former shareholders of the Predecessor Fund received Class I shares of the Fund. The Predecessor Fund was advised by Investment Counselors of Maryland, LLC, which was acquired by the Adviser. The Predecessor Fund’s (Institutional Class shares) performance and financial history has been adopted by Class I shares of the Fund following the Reorganization and will be used going forward from the date of the Reorganization. The performance of Class I shares of the Fund therefore reflects the performance of the Predecessor Fund prior to the Reorganization. The performance of the Predecessor Fund has not been restated to reflect the annual operating expenses of Class I shares of the Fund, which were different than those of the Predecessor Fund. Because the Fund had different fees and expenses than the Predecessor Fund, the Predecessor Fund would therefore have had different performance results if it was subject to the Fund’s fees and expenses. The Fund’s past performance (including the performance of the Predecessor Fund), before and after taxes, is not necessarily an indication of how the Fund will perform in the future and does not guarantee future results. For more recent performance information, go to www.williamblairfunds.com or call 1‑800‑635‑2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class I shares.


		Highest Quarterly Return 29.75% (4Q20)		Lowest Quarterly Return (35.02)% (1Q20)

Average Annual Total Returns (For the periods ended December 31, 2021). The table below shows returns on a before‑tax and after‑tax basis for Class I shares. After‑tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after‑tax returns depend on an investor’s tax situation and may differ

from those shown. After‑tax returns are not relevant to investors who hold their Fund shares through tax‑deferred arrangements, such as 401(k) plans or individual retirement accounts.

Because the Predecessor Fund did not offer share classes other than Institutional Class shares, no performance information is shown for Class R6 or Class N shares of the Fund. Performance information for those classes will be provided after a full calendar year of performance history following the Reorganization is available.


	1 Year		5 Years		10 Years
Class I Shares
Return Before Taxes		29.49%		10.33%		13.03%
Return After Taxes on Distributions		24.71%		7.96%		10.50%
Return After Taxes on Distributions and Sale of Fund Shares		19.14%		7.52%		10.01%

Russell 2000^® Value Index (reflects no deduction for fees, expenses or taxes)		28.27%		9.07%		12.03%

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). William V. Heaphy, CFA, an Associate of the Adviser, and Gary J. Merwitz, an Associate of the Adviser, co‑manage the Fund. Mr. Heaphy and Mr. Merwitz have each co‑managed the Fund since 2021 (and managed the Predecessor Fund since 1999 and 2004, respectively).

PURCHASE AND SALE OF FUND SHARES:

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

WILLIAM BLAIR GLOBAL LEADERS FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair Global Leaders Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):

Class N

Class I

Class R6

Maximum Sales Charge (Load) Imposed on Purchases

None

Redemption Fee

None

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


	Class N		Class I		Class R6
Management Fee		0.85%		0.85%		0.85%
Distribution (Rule 12b‑1) Fee		0.25%		None		None
Other Expenses		0.28%		0.22%		0.14%

Total Annual Fund Operating Expenses		1.38%		1.07%		0.99%
Fee Waiver and/or Expense Reimbursement*		0.23%		0.17%		0.14%

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		1.15%		0.90%		0.85%


	1 Year		3 Years		5 Years		10 Years
Class N		$117		$414		$733		$1,637
Class I		92		323		574		1,290
Class R6		87		301		533		1,200

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its total assets in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes worldwide that the Adviser believes have above-average growth, profitability and quality characteristics. The Adviser seeks investment opportunities in companies at different stages of development, ranging from large, well-established companies to smaller companies at earlier stages of development, that are leaders in their country, industry or globally in terms of products, services or execution. The Fund’s investments are normally allocated among at least six different countries and no more than 65% of the Fund’s equity holdings may be invested in securities of issuers in any one country at any given time. Under normal market conditions, at least 40% of the Fund’s assets will be invested in companies located outside the United States. Normally, the Fund’s investments will be divided among the United States, Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 30% of its net assets or twice the emerging markets component of the MSCI All Country World Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.

In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.

The Adviser will vary the Fund’s sector and geographic diversification based upon the Adviser’s ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Adviser will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of companies throughout the world, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

infectious illness or other public health threats could also significantly impact the Fund and its investments. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.

Foreign Investment Risk. The risks of foreign investments may include less publicly available information, less stringent investor protections and disclosure standards, less governmental regulation and supervision of foreign stock exchanges, brokers and issuers, share registration and custody, a lack of uniform accounting, auditing and financial reporting standards, practices and requirements, the possibility of expropriation, seizure or nationalization, confiscatory taxation, limits on repatriation, adverse changes in investment or exchange control regulations, political instability, restrictions on the flow of international capital, imposition of foreign withholding or other taxes, fluctuating currencies, inflation, difficulty in obtaining and enforcing judgments against foreign entities or other adverse political, social or diplomatic developments that could affect the Fund’s investments. Foreign investments may be less liquid and their prices more volatile than the securities of U.S. companies. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments.

Currency Risk. The value of the Fund’s portfolio may be affected by changes in exchange rates or control regulations. If a local currency gains against the U.S. dollar, the value of the security increases in U.S. dollar terms. If a local currency declines against the U.S. dollar, the value of the security decreases in U.S. dollar terms.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.

Geographic Risk. To the extent that the Fund invests a significant portion of its assets in any one country or geographic region, the Fund will be subject to greater risk of loss or volatility than if the Fund always maintained wide geographic diversity among the countries and geographic regions in which it invests. Investing in any one country or geographic region makes the Fund more vulnerable to the risks of adverse securities markets, exchange rates and social, political, regulatory and economic events in that one country or geographic region.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.


		Highest Quarterly Return 24.59% (2Q20)		Lowest Quarterly Return (17.96)% (1Q20)


	1 Year		5 Years		10 Years
Class N Shares
Return Before Taxes		16.55%		19.25%		13.84%
Return After Taxes on Distributions		15.02%		17.17%		12.70%
Return After Taxes on Distributions and Sale of Fund Shares		10.84%		15.16%		11.34%

Class I Shares
Return Before Taxes		16.78%		19.55%		14.15%

MSCI All Country World IMI (net) (reflects no deduction for fees, expenses or taxes)		18.22%		14.12%		11.84%


	1 Year		5 Years		Since Share Class Inception (December 19, 2012)
Class R6 Shares
Return Before Taxes		16.90%		19.62%		13.76%

MSCI All Country World IMI (net) (reflects no deduction for fees, expenses or taxes)		18.22%		14.12%		11.26%

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Andrew G. Flynn, a Partner of the Adviser, Kenneth J. McAtamney, a Partner of the Adviser, and Hugo Scott-Gall, a Partner of the Adviser, co‑manage the Fund. Mr. Flynn has co‑managed the Fund since 2016. Mr. McAtamney has co‑managed the Fund since 2008. Mr. Scott-Gall has co‑managed the Fund since 2021.

PURCHASE AND SALE OF FUND SHARES:

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

WILLIAM BLAIR INTERNATIONAL LEADERS FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair International Leaders Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):

Class N

Class I

Class R6

Maximum Sales Charge (Load) Imposed on Purchases

None

Redemption Fee

None

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


	Class N		Class I		Class R6
Management Fee		0.85%		0.85%		0.85%
Distribution (Rule 12b‑1) Fee		0.25%		None		None
Other Expenses		0.20%		0.14%		0.06%

Total Annual Fund Operating Expenses		1.30%		0.99%		0.91%
Fee Waiver and/or Expense Reimbursement*		0.15%		0.09%		0.06%

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		1.15%		0.90%		0.85%


	1 Year		3 Years		5 Years		10 Years
Class N		$117		$397		$699		$1,555
Class I		92		306		538		1,205
Class R6		87		284		498		1,114

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes domiciled outside the U.S. that the Adviser believes have above-average growth, profitability and quality characteristics. Under normal market conditions, the Fund typically holds a limited number of securities (i.e., 40‑70 securities). The Adviser seeks investment opportunities in companies at different stages of development ranging from large, well-established companies to smaller companies at earlier stages of development, that are leaders in their country, industry or globally in terms of products, services or execution. The Fund’s investments are normally allocated among at least six different countries and no more than 50% of the Fund’s equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund’s investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 40% of its net assets or twice the emerging markets component of the MSCI All Country World Ex‑U.S. Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of foreign companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

Focus Risk. To the extent that the Fund focuses its investments in particular industries, asset classes or sectors of the economy, any market changes affecting companies in those industries, asset classes or sectors may impact the Fund’s performance. In addition, because the Fund may focus its investments in a limited number of securities, its performance may be more volatile than a fund that invests in a greater number of securities.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the calendar years since the Fund started for Class N shares.


		Highest Quarterly Return 21.43% (2Q20)		Lowest Quarterly Return (18.69)% (1Q20)


	1 Year		5 Years		Life of the Fund (since August 16, 2012)
Class N Shares
Return Before Taxes		9.93%		15.64%		11.46%
Return After Taxes on Distributions		9.24%		15.14%		11.08%
Return After Taxes on Distributions and Sale of Fund Shares		6.35%		12.53%		9.39%

Class I Shares
Return Before Taxes		10.17%		15.95%		11.73%

MSCI All Country World Ex‑US IMI (net) (reflects no deduction for fees, expenses or taxes)		8.53%		9.83%		7.24%


	1 Year		5 Years		Since Share Class Inception (November 2, 2012)
Class R6 Shares
Return Before Taxes		10.22%		16.01%		11.83%

MSCI All Country World Ex‑US IMI (net) (reflects no deduction for fees, expenses or taxes)		8.53%		9.83%		6.98%

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Alaina Anderson, a Partner of the Adviser, Simon Fennell, a Partner of the Adviser, and Kenneth J. McAtamney, a Partner of the Adviser, co‑manage the Fund. Ms. Anderson has co‑managed the Fund since 2021. Mr. Fennell has co‑managed the Fund since 2013. Mr. McAtamney has co‑managed the Fund since its inception in 2012.

PURCHASE AND SALE OF FUND SHARES:

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

WILLIAM BLAIR INTERNATIONAL GROWTH FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair International Growth Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):

Class N

Class I

Class R6

Maximum Sales Charge (Load) Imposed on Purchases

None

Redemption Fee

None

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


	Class N		Class I		Class R6
Management Fee*		0.94%		0.94%		0.94%
Distribution (Rule 12b‑1) Fee		0.25%		None		None
Other Expenses		0.20%		0.13%		0.05%

Total Annual Fund Operating Expenses		1.39%		1.07%		0.99%
Fee Waiver and/or Expense Reimbursement**		0.15%		0.08%		0.05%

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement***		1.24%		0.99%		0.94%

*	The Management Fee has been restated to reflect a reduction to 0.94% of average daily net assets effective May 1, 2022.

***	The Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement does not equal the net expense ratio to average daily net assets in the Financial Highlights section of this prospectus as a result of a change in the management fee and contractual expense limits.


	1 Year		3 Years		5 Years		10 Years
Class N		$126		$425		$746		$1,656
Class I		101		332		582		1,298
Class R6		96		310		542		1,208

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its total assets in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes domiciled outside the U.S. that the Adviser believes have above-average growth, profitability and quality characteristics. The Adviser seeks investment opportunities in companies at different stages of development ranging from large, well-established companies to smaller companies at earlier stages of development. The Fund’s investments are normally allocated among at least six different countries and no more than 50% of the Fund’s equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund’s investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 35% of its net assets or twice the emerging markets component of the MSCI All Country World Ex‑U.S. Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.


		Highest Quarterly Return 25.20% (2Q20)		Lowest Quarterly Return (19.91)% (1Q20)


	1 Year		5 Years		10 Years
Class N Shares
Return Before Taxes		8.68%		14.56%		10.49%
Return After Taxes on Distributions		5.82%		13.36%		9.71%
Return After Taxes on Distributions and Sale of Fund Shares		6.96%		11.50%		8.49%

Class I Shares
Return Before Taxes		9.01%		14.90%		10.82%

MSCI All Country World Ex‑U.S. IMI (net) (reflects no deduction for fees, expenses or taxes)		8.53%		9.83%		7.57%


	1 Year		Since Share Class Inception (May 2, 2019)
Class R6 Shares
Return Before Taxes		9.09%		19.56%

MSCI All Country World Ex‑U.S. IMI (net) (reflects no deduction for fees, expenses or taxes)		8.53%		10.14%

MANAGEMENT:

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Simon Fennell, a Partner of the Adviser, Kenneth J. McAtamney, a Partner of the Adviser, and Andrew Siepker, CFA, a Partner of the Adviser, co‑manage the Fund. Mr. Fennell has co‑managed the Fund since 2013. Mr. McAtamney has co‑managed the Fund since 2017. Mr. Siepker has co‑managed the Fund since 2022.

PURCHASE AND SALE OF FUND SHARES:

Purchase. The Fund is closed to new investors. Shares are only available to certain investors. In certain circumstances, existing shareholders may be able to open a new Fund account for a different share class. See “Your Account—International Growth Fund, Institutional International Growth Fund, International Small Cap Growth Fund and Emerging Markets Small Cap Growth Fund” for information on eligibility requirements applicable to purchasing shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

WILLIAM BLAIR INSTITUTIONAL INTERNATIONAL GROWTH FUND

SUMMARY

INVESTMENT OBJECTIVE: The William Blair Institutional International Growth Fund seeks long-term capital appreciation.

Shareholder Fees (fees paid directly from your investment):


Maximum Sales Charge (Load) Imposed on Purchases			None
Redemption Fee			None

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


Management Fee*			0.94%
Distribution (Rule 12b‑1) Fee			None
Other Expenses			0.05%

Total Annual Fund Operating Expenses			0.99%
Fee Waiver and/or Expense Reimbursement**			0.05%

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement***			0.94%

*	The Management Fee has been restated to reflect a reduction to 0.94% of average daily net assets effective May 1, 2022.

***	The Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement does not equal the net expense ratio to average daily net assets in the Financial Highlights section of this prospectus as a result of a change in the management fee and contractual expense limits.


1 Year	3 Years	5 Years	10 Years
$96	$310	$542	$1,208