The earliest monetary fund in the United States was established in 197 1 year. At that time, the original intention of establishing the monetary fund was to avoid the "Q rule". At that time, the Q regulation prohibited banks from paying interest on demand deposits, and set interest rate ceilings on various bank deposits, which made it impossible for commercial banks to attract depositors' funds by using interest rates. As a result, the monetary fund came into being. By pooling investors' funds, it invests the pool of funds in some short-term securities such as US Treasury bonds and some commercial papers, and then returns the interest income to investors, thus becoming a substitute for bank demand deposits.

The net value of money market funds is always 1 USD (China is 1 RMB), but during the financial crisis, the net value of American money funds did fall to 1 USD, which was due to the bankruptcy of Lehman Brothers, which led to the bad debts of corporate debt bills held by the money funds. This news once caused panic in the money fund market, and some money funds even ran. Soon, the US Treasury Department announced that eligible money markets and funds can join an insurance-like project by paying a certain fee, which can ensure that when the money fund falls to the net value of 1 USD, the net value will be restored to 1 USD (of course, there are some additional conditions on assets). This project is somewhat similar to the federal deposit insurance in the United States, which quickly stabilized the money fund market. However, this insurance mechanism retreated from the financial market in 2009 when the market was stable.