Unlike Discover and American Express, which issue their own cards, Visa and Mastercards are issued by banks. The banks make profit on the credit cards in two ways: 1. On every transaction they collect a fee from the merchant called an interchange fee 2. They charge interest and other fees to the cardholder. There are thousands of issuing banks, but the market in the US is heavily dominated by a few large firms: List of Largest Credit Card Issuers in 2006.