One of the main US credit-rating agencies. It produces the S&P 500 stock price index, based on the prices of 500 principal shares traded on the New York Stock Exchange (NYSE). This covers about 80 percent of the total value of stocks traded. The S&P 100 index covers many of the larger corporations' stocks, representing about 60 percent of the NYSE market.
http://www.standardandpoors.com Access to the credit rating services and other products of Standard and Poor's.