S&P 500 - short for Standard and Poor's 500, is a United States stock market index based on the market capitalizations of the top 500 companies that have common stock listed on the New York Stock Exchange or NASDAQ. With its headquarters in New York City and dating back to 1860, Standard and Poor's has offices in 23 countries and maintains the SP 500 index. Over $1.25 trillion USD is indexed to Standard and Poor's portfolio of indices, which includes the S&P 500. The S&P500 index seeks to reflect the status of the whole stock market by tracking the return and volatility of the 500 most commonly held large cap company stocks on the NYSE, capturing approximately 80% of total market capitalization. The 500 companies comprising the SP500 span all major industries and are selected based on their market capitalization, liquidity, ability to be traded, as well as other factors. Additionally, the importance of the SP500 is highlighted by its use as an economic indicator of the health of the United States economy.