A man walks past the charging bull statue near the New York Stock Exchange.
Mandel Ngan | AFP | Getty Images
The S&P 500 index measures the performance of 500 of the largest publicly traded companies on stock exchanges in the U.S. These companies span 11 different market sectors, representing the various industries powering the U.S. economy. The S&P 500, a key benchmark for U.S. equities more broadly, has an overall market value of $37.28 trillion, according to FactSet.