A casino is an establishment where people can gamble and play games of chance or skill. Some casinos specialize in particular games, such as blackjack or poker, while others offer a wide variety of games. The largest concentration of casinos is in the United States, with most located in Nevada, followed by Atlantic City and Chicago.

The exact origins of gambling are unknown, but it is believed to have existed in many societies throughout history. Modern casino gambling is based on the use of electronic machines, such as slot machines and video poker, to generate random numbers that are compared with the paytable to determine winnings. A percentage of the money bet is taken by the casino as a commission, known as the house edge or vigorish. In addition to this mandatory fee, some casinos give out complimentary items or comps to their players.

Casinos spend large amounts of money on security, and employ a variety of techniques to prevent cheating, stealing and collusion between patrons. Security personnel on the floor keep a close eye on all activities, and pit bosses and table managers watch for signs of cheating at table games such as palming, marking and crooked dice. Catwalks in the ceiling above the casino floor allow surveillance personnel to look directly down, through one-way glass, on activities at individual tables and slots.

Because each game has a built-in advantage for the casino, it is very rare for a casino to lose money on any given day. Because of this virtual guarantee of gross profit, casinos are able to offer big bettors extravagant inducements such as free shows, hotel rooms and transportation.