A casino, or gambling house, is a place where people can gamble and play games of chance. Most casinos also offer restaurants, bars, retail shops, and other tourist attractions. In some countries, casinos are the only legal places where certain types of gambling can take place.

There are approximately 3,000 casinos in the world. The majority of these are located in the United States, with more than half of them in Las Vegas. Other major casino locations include Atlantic City, New Jersey; Detroit, Michigan; and Puerto Rico. Casinos may also be found on American Indian reservations, as they are exempt from state antigambling laws.

Many people visit casinos to gamble, but the vast majority do not become addicted. Compulsive gamblers are a small minority that generates a disproportionate amount of casino profits. Economic studies suggest that compulsive gambling reduces community spending on other forms of entertainment, and the social costs of treating problem gamblers offset any positive economic effects a casino might have.

Casinos make money by charging a percentage of bets to players, called the house edge. This can be a very small percentage of the total amount wagered, but it adds up over time and allows casinos to build elaborate hotels, fountains, towers, and replicas of famous landmarks.

In the modern sense of the word, casinos specialize in slot machines, which account for a large share of their income. These devices are very simple to operate; the player simply inserts cash or paper tickets with barcodes and presses a button to spin the reels. Varying bands of colored shapes roll past on the reels (actual physical ones or a video representation of them). If the right pattern appears, the machine pays out a predetermined amount of money. In addition to slot machines, most casinos offer table games such as blackjack and roulette.

Something about the environment of a casino seems to encourage cheating and stealing, both by patrons and staff members. As a result, most casinos devote significant resources to security. Modern casinos have a dedicated physical security force and a specialized department for surveillance, known as the eye in the sky.

In terms of revenue, the largest casinos in the world are in Las Vegas, followed by Atlantic City and Chicago. In recent years, however, a number of other cities have begun to rival these gaming centers. In addition, more and more states are legalizing casinos. The number of legal casinos in the United States now stands at over 40. This trend is expected to continue.