In 2002, about 51 million people—about a quarter of Americans over the age of 21—visited a casino. That’s a lot of money—and some of it was spent on compulsive gambling, which subtracts from the net income of casinos.

Casinos make money by charging patrons to play games of chance, or skill—such as baccarat and blackjack. Most games have a built-in mathematical advantage for the casino, which can be less than two percent. This slight edge—often called the vig or rake—gives casinos enough money to build huge hotels, fountains, towers, and replicas of famous landmarks.

Gambling is more than a business; it taps into a deep-seated human need for the thrill of risk. This is why casinos are so popular, from the glitzy Las Vegas strip to the illegal pai gow parlors in New York City’s Chinatown.

Besides offering high-stakes gambling, casinos provide food, drink, and entertainment. They also have elaborate security systems, with cameras that watch every table, doorway, and window, and can be shifted to focus on suspicious patrons. Security personnel use a language of patterns to spot cheating: the way dealers shuffle and deal cards, for example, or the expected reactions to particular betting patterns.

The business of casinos is complex, and it’s difficult to gauge how much money they actually make. However, there are plenty of other economic benefits: Casinos lure tourists, who spend money on hotel rooms, restaurants, and other attractions; they help boost local property values; and they employ many people. But critics say that the money spent treating problem gamblers and lost productivity by those who can’t control their gambling can undo any gains a casino might make for its community.