Standard & Poor’s (S&P) created its first stock index in 1923, the S&P 90.  Although S&P published a weekly index of over 400 companies, the value-weighted S&P 90 index was based on 90 of the most dominant stocks of time.  Technological advancements in the 1950s allowed S&P to drastically increase the number of stocks included in its index.

On this day, March 4th, in 1957, the S&P 500 stock market index is introduced, replacing the S&P 90.  As a result of recently developed computer technology, the S&P 500 was calculated and dispersed in real time. The S&P 500 featured a free-float capitalization-weighted index and included 500 large-cap common stocks traded in the United States.  Most large, publicly held companies traded on the New York Stock Exchange and the NADSAQ are included in the S&P 500.

The index has grown to include some non-U.S. companies. Companies included in the S&P 500 are chosen by committee and are intended to reflect the industries in the U.S. economy.  The S&P 500 is still in use today and is considered the second most followed stock index, after the Dow Jones Industrial Average.