The Standard and Poor's 500 (S&P 500) is a stock market index tracking the stock performance of 500 of the largest companies listed on stock exchanges in the United States. It includes approximately 80% of the total market capitalization of U.S. public companies, with an aggregate market cap of more than $43 trillion as of January 2024. The S&P 500 index is a free-float weighted/capitalization-weighted index.