Money funds (or money market funds, money market mutual funds) are mutual funds that invest in short-term debt instruments. Institutional money fund Institutional money funds are usually set up so that money is swept to them overnight from a company's main operating accounts. Large national chains often have many accounts with banks all across the country, but electronically pull a majority of funds on deposit with them to a concentrated money market fund. Retail money funds One of the largest money market mutual funds is Fidelity Investments' Cash Reserves, with assets exceeding $71 billion.