A mutual fund is a type of professionally-managed collective investment scheme that pools money from many investors to purchase securities. While there is no legal definition of mutual fund, the term is most commonly applied only to those collective investment schemes that are regulated, available to the general public and open-ended in nature. Hedge funds are not considered a type of mutual fund.

The term mutual fund is less widely used outside of the United States. For collective investment schemes outside of the United States, see articles on specific types of funds including open-ended investment companies, SICAVs, unitized insurance funds, unit trusts and Undertakings for Collective Investment in Transferable Securities.

In the United States, mutual funds must be registered with the Securities and Exchange Commission, overseen by a board of directors or board of trustees and managed by a registered investment advisor. They are not taxed on their income if they comply with certain requirements.