Credit cards have become the most popular medium for exchanging money in today's society. The largest credit card company is Visa, and they process $15 billion of transactions per day on average, with a total yearly volume near $5 trillion. Visa accounts for 40% of the credit card market, so the total amount of money transacted via credit cards easily exceeds $10 trillion each year. This is nearly as much as the gross domestic product (GDP) of the United States.