The S&P 500 (Standard & Poor's) is a free-float capitalization-weighted index published since 1957 of the prices of 500 large-cap common stocks actively traded in the United States. The stocks included in the S&P 500 are those of large publicly held companies that trade on either of the two largest American stock market exchanges; the NYSE Euronext (纽约证券交易所) and the NASDAQ OMX （纳斯达克）.

After the Dow Jones Industrial Average, the S&P 500 is the most widely followed index of large-cap American stocks. It is considered a bellwether for the American economy, and is included in the Index of Leading Indicators. Many mutual funds, exchange-traded funds, and other funds such as pension funds, are designed to track the performance of the S&P 500 index. Hundreds of billions of US dollars have been invested in this fashion.

标准普尔500指数英文简写为S&P 500 Index，是记录美国500家上市公司的一个股票指数。这个股票指数由标准普尔公司创建并维护。

　　标准普尔500指数覆盖的所有公司，都是在美国主要交易所，如纽约证券交易所、Nasdaq交易的上市公司。与道琼斯指数相比，标准普尔500指数包含的公司更多，因此风险更为分散，能够反映更广泛的市场变化。

　　标准·普尔500指数是由标准·普尔公司1957年开始编制的。最初的成份股由425种工业股票、15种铁路股票和60种公用事业股票组成。从1976年7月1日开始，其成份股改由400种工业股票、20种运输业股票、40种公用事业股票和40种金融业股票组成。它以1941年至1942年为基期，基期指数定为10，采用加权平均法进行计算，以股票上市量为权数，按基期进行加权计算。与道·琼斯工业平均股票指数 （Dow Jones Industrial Average）相比，标准·普尔500指数具有采样面广、代表性强、精确度高、连续性好等特点，被普遍认为是一种理想的股票指数期货合约的标的。