Investing in the index is when you seek to replicate and hold a broad market index such as the S&P 500 or the S&P/TSX Composite Index. These indexes are a collection of stocks/companies. For example, the S&P 500 holds the 500 large-cap U.S. companies in proportion to their size (market cap). In index investing, you are looking to match the returns of the broad market rather than trying to beat the market.