There are thousands of stock market indexes in the United States, but the three most widely followed are the S&P 500, the Dow Jones Industrial Average, and the Nasdaq Composite Index.  S&P 500 Established in 1957, the S&P 500 was the first market-capitalization-weighted index in the US. It includes 500 of the nation's largest public companies and is worth about 80% of the US stock market's total value. Often, this index is seen as synonymous with the state of US stock markets, and of business overall. Dow Jones Industrial Average  The Dow Jones Industrial Average (DJIA) is one of the oldest stock market indexes in the US, dating back to 1896. It's also one of the smallest, including just 30 corporations. You may also hear them referred to as blue-chip companies. The DJIA is price-weighted, and like the S&P 500, it's often used to gauge the performance of the overall stock market and US economy. Nasdaq Composite Index  The Nasdaq Composite Index is the relatively new kid on the block, established in 1971. Primarily focused on the technology sector — though it also includes some financial, industrial, insurance, and transportation stocks — it contains about 3,000 companies. Stocks are market-capitalization-weighted, and all the companies in the index are traded on the Nasdaq stock exchange, but not all of them are based in the US. Other prominent stock market indexes