A money market fund (also called a money market mutual fund) is an open-ended mutual fund that invests in short-term debt securities such as US Treasury bills and commercial paper. Money market funds are widely (though not necessarily accurately) regarded as being as safe as bank deposits yet providing a higher yield. Regulated in the United States under the Investment Company Act of 1940, money market funds are important providers of liquidity to financial intermediaries.
Money market funds seek to limit exposure to losses due to credit, market, and liquidity risks. Money market funds in the United States are regulated by the Securities and Exchange Commission (SEC) under the Investment Company Act of 1940. Rule 2a-7 of the act restricts the quality, maturity and diversity of investments by money market funds. Under this act, a money fund mainly buys the highest rated debt, which matures in under 13 months. The portfolio must maintain a weighted average maturity (WAM) of 60 days or less and not invest more than 5% in any one issuer, except for government securities and repurchase agreements.
Unlike most other financial instruments, money market funds seek to maintain a stable value of $1 per share. Funds are able to pay dividends to investors.
Securities in which money markets may invest include commercial paper, repurchase agreements, short-term bonds and other money funds. Money market securities must be highly liquid and of the highest quality.