The S&P 500 Index explained Table of Contents:IntroductionS&P 500 FAQsS&P 500 Annual ReturnsS&P 500 Current List of StocksFinal ThoughtsIntroductionThe S&P 500 was founded in 1957.  The S&P 500 is closely watched by market analysts and the media since its performance represents a gauge into the health or lack there of for the U.S. economy.The S&P (Standards and Poor's) 500 includes 505 common