The S&P 500, launched in its modern form in 1957, became a principal benchmark during the 2008 market crash.
Standard & Poor’s introduced the modern 500-stock index on March 4, 1957. It tracks large U.S. companies across many industries and is weighted by market capitalization, meaning companies with greater total market value have greater influence on the index. Because of that broad coverage, financial professionals frequently use it as a gauge of U.S. large-cap equities.
During the global financial crisis, the S&P 500 fell sharply as mortgage losses, bank failures, recession fears, and forced selling damaged confidence. It reached a major closing low of 676.53 on March 9, 2009, after having peaked in October 2007.
The index is not the same as the Dow, which contains 30 companies and uses a price-weighting method. Nor is it identical to the Nasdaq Composite, which includes thousands of Nasdaq-listed securities and has a stronger technology emphasis.