The S&P 500 is one of the most followed indices of large-cap American stocks, tracking the performance of 500 companies based in the US.
Traders and investors will follow the S&P 500 closely, as is perceived to be an indicator of the health of the country’s economy as a whole. The firms on this index are traded on the Nasdaq or the New York Stock Exchange.
The index reached its highest ever close in 2018, at the top of the Bull Run that started after the lows of the economic crisis, hitting 2,930.75.
S&P offers other indices including the S&P 400 (which measures the performance of companies with market capitalisation of $2 billion - £10 billion) and the S&P 600 ($300 million - $2 billion).
Companies in index: Apple, Chevron, Exxon Mobil, JP Morgan.