Massachusetts Investors Trust (now MFS Investment Management) was founded on March 21, 1924, and, after one year, had 200 shareholders and $392,000 in assets. The entire industry, which included a few closed-end funds, represented less than $10 million in 1924. The stock market crash of 1929 slowed the growth of mutual funds.

In response to the stock market crash, the Congress passed the Securities Act of 1933 and the Securities Exchange Act of 1934.

These laws require that a fund be registered with the Securities and Exchange Commission (SEC) and provide prospective investors with a prospectus that contains required disclosures about the fund, the securities themselves, and fund manager.

The SEC helped draft the Investment Company Act of 1940, which sets forth the guidelines with which all SEC-registered funds today must comply.

With renewed confidence in the stock market, mutual funds began to blossom. By the end of the 1960s, there were approximately 270 funds with $48 billion in assets.

The first retail index fund, the First Index Investment Trust, was formed in 1976 and headed by John Bogle, who conceptualized many of the key tenets of the industry in his 1951 senior thesis at Princeton University.

It is now called the Vanguard 500 Index Fund and is one of the largest mutual funds ever with over $100 billion in assets.