The answer is no, not all 30 Dow stocks are in the S&P 500. In fact, only about half of them are. The reason for this is that the S&P 500 is a market cap-weighted index, meaning that the companies with the highest market capitalizations make up a larger percentage of the index. And since the Dow is price-weighted (meaning each stock's weight in the index is based on its share price), it generally includes smaller companies than the S&P 500.