Invest in S&P 500 Exchanged-Traded Fund (ETF) S&P 500 Index measures the stock performance of the largest 500 companies listed on stock exchanges in the United States. Companies such as Amazon, Apple, McDonald's, Microsoft, Google, Coca-Cola and Netflix are included in this list. You see that if you invest in S&P 500, you pretty much have invested in the top companies in the world. This is why S&P 500 is commonly referred to as 'the market'. This list of the largest 500 compa