Definition: Money market mutual funds allow the average investor access to the rewards and relative safety of a variety of money market instruments. That's because these funds only invest in low-risk securities. Since they are low risk, and they generally invest in short-term securities, they pay the very low dividends or interest that usually reflects short-term interest rates.

How Do Money Market Funds Work?

These funds took off in the 1970s, and have grown to nearly $3 trillion in total assets.

Most money market instruments require investments of around $100,000 because they are geared to large businesses, banks and the government. Money market funds can buy these investments, and then sell shares to the public.

What Do They Invest In?

Money markets invest in three types of low-risk securities. The first is U.S. Treasury bills, which are backed by the federal government.

The second is certificates of deposit, 

The third is commercial paper of very solid companies. This is short-term debt that large companies can issue instead of going to the bank for a loan. Only well-regarded companies can do this, because the debt is nothing more than a promise from the company that it will be repaid. There are no assets backing the loan. However, the company usually has enough outstanding invoices, known as receivables, to support the loan. It just needs the money now to pay for day-to-day operations until future payments for orders come in. It's like a payday loan for business. The company promises it will repay the debt within a year, if not sooner.

 

Advantages

Money market funds are usually very safe. They allow easy access to the cash invested, and they don't require a minimum. Their rates are slightly below those of CDs that levy penalties if funds are withdrawn before they come due.

Disadvantages

When interest rates are low, they may pay less than the rate of inflation. When that happens, fund investors are actually losing their purchasing power. However, many cannot afford to take the risk required to stay ahead of inflation, such as stocks, corporate bonds or hi-yield mutual funds.

Unlike bank money market accounts, they are not insured by the FDIC (Federal Deposit Insurance Corporation).

How Are They Different From Other Mutual Funds?

Unlike mutual funds that are invested in stocks, money market funds usually try to keep the net asset value of (NAV) of each share at a dollar. They are allowed to do so because they are invested in safe, short-term debt. This allows their investors to avoid changing the value on the books every day. They pay interest instead. Therefore, the value of the money market fund is dependent on the yield or interest rate, which does vary. It is very rare for the NAV to fall below a dollar, called breaking the buck, but it can happen if the investments do poorly.

When Money Markets Funds Almost Failed

This is what happened on September 16, 2008, to the $62 billion Reserve Primary Fund, the nation's oldest money market fund. The money market had invested in Lehman Brothers short-term debt, and when that investment bank went bankrupt, Reserve's NAV dropped to 97 cents. Since it was the first money fund in 14 years to break the buck, it caused panicked investors to withdraw $139 billion out of money market funds in the next two days, according to IMoneyNet.

As a result, on September 19, 2008, the Treasury Department stepped in to guarantee money market funds. This run on money market funds made Treasury SecretaryHenry Paulson realize that credit markets were shutting down, and he needed to submit the $700 billion bailout bill to Congress. On October 21, the Federal Reserve agreed to buy assets from money market funds who needed cash to pay for redemptions. (Source: SEC, Money Market Funds) Article updated March 20, 2015.