Index Funds -An index fund is a type of mutual fund that builds its portfolio by buying stock in all the companies of a particular index and thereby reproducing the performance of an entire section of the market. The most popular index of stock index funds is the Standard & Poor’s 500. An S&P 500 stock index fund owns 500 stocks-all the companies that are included in the index. Investing in an index fund is a form of passive investing. Passive investing has two big advantages over active investing. First, a passive stock market mutual fund is much cheaper to run than an active fund. Second, a majority of mutual funds fail to beat broad indexes such as the S&P 500.