What is the S&P 500 -- Should you Invest in the S&P 500 You've probably heard about the S&P 500 stock market index. It's what most people consider to be "the market" and it gives us good insight as to what the entire stock market is doing. What exactly does S&P 500 mean? This index is made up of a variety of companies of various sectors. For those of us that don't know much about investing, it can be a great choice providing the diversification needed for a well rounded portfolio in just one product. However, depending on your circumstances, there are better choices. When should you choose the S&P 500 and when should you seek alternatives? Take a look at what companies make up this index and its pros and cons to decide if it's the right choice for you.