Imagine trying to buy a tiny piece of every major company in the U.S. stock market. It sounds complicated and expensive, right? An index fund does this for you. It's a type of investment that holds a collection of stocks designed to mimic a specific market index, like the S&P 500.

An index is just a list of investments that represents a slice of the market. For example, the S&P 500 includes 500 of the largest U.S. companies. When you buy a share of an S&P 500 index fund, you're buying a small, diversified slice of all those companies at once. The goal isn't to beat the market, but to match its performance. If the S&P 500 goes up by 10%, your index fund investment should also go up by about 10%, minus a very small fee.

This approach is the core of a popular investment style called passive investing.

Investing strategies generally fall into two camps: passive and active. Think of it like fishing. An active investor tries to catch specific, prize-winning fish, believing they can find the best ones. A passive investor simply casts a wide net and catches a bit of everything that swims by.

Active management involves a fund manager or team of experts actively researching and selecting investments they believe will outperform the market. They buy and sell stocks, bonds, or other assets based on their analysis, trying to generate higher returns than a benchmark index. This hands-on approach usually comes with higher fees to pay for the research and frequent trading.

Passive management, on the other hand, is a “set it and forget it” strategy. Instead of trying to pick winners, passive funds simply buy and hold all the investments in a particular index. Because there's no need for constant research or trading, the costs are typically much lower.

The key difference is the belief about whether it's possible to consistently beat the market. Active managers believe they can. Passive investors are content with capturing the market's average return, which historically has been quite good over the long term.

The idea of an index fund wasn't always mainstream. For decades, the investment world was dominated by active managers who prided themselves on their stock-picking skills.

In the 1960s and 70s, academic research began to show that very few active managers consistently beat the market averages over long periods, especially after accounting for their higher fees. This led to a revolutionary idea: what if you could just buy the average?

John C. Bogle, the founder of The Vanguard Group, acted on this idea. In 1976, he launched the first index fund available to the general public. It was initially mocked by the industry as “Bogle’s Folly” and criticized for being “un-American” by aiming for average returns. Despite the slow start, the fund's low costs and steady, market-matching performance eventually won over millions of investors. This simple idea has since transformed the investment industry, making diversified, low-cost investing accessible to everyone.

Now that you know what index funds are and where they came from, let's test your understanding.

By embracing a passive strategy, index funds provide a straightforward way to participate in the growth of the broader market without needing to become a stock-picking expert.