Money market funds are fixed income mutual funds that invest in debt securities characterized by short maturities and minimal credit risk. They are among the lowest-volatility types of investments. For money market funds, income generated is either taxable or tax-exempt, depending on the types of securities in which the fund invests. These may include short-term U.S. Treasury securities, federal agency notes, Eurodollar deposits, repurchase agreements, certificates of deposit, corporate commercial paper; or obligations of states, cities, or other types of municipal agencies.