Since the S&P 500 is generally used as an indication of the health of the entire U.S market, its components come from a wide variety of different industries. It tracks the common stocks issued by 500 large-cap US companies. A combination of selection criteria and stock performance is used to determine which 500 companies make the list. Standard & Poor’s provides comprehensive criteria. But to give a broad overview, a company must meet the following requirements: A market cap of $5.3b or more Be headquartered in the US and publicly trade its stocks on one of a selection of US stock exchanges Must trade at least the value of its market capitalization annually Must public float at least 50% of its stock Must have had its IPO at least 6 months ago Must have had 4 straight quarters of reported growth The S&P 500 is adjusted on an as-needed basis, meaning that there is no specified schedule for additions or removals. As of the time of writing the top 5 stocks are: Apple Inc. (AAPL) Microsoft Corp (MSFT) Exxon Mobil Corp (XOM) Amazon.com Inc (AMZN) Berkshire Hathaway B (BRK.B)