A casino is a place where people can gamble with money or other items of value. Most casinos offer a wide variety of gambling games, such as poker, blackjack, and roulette. Some casinos also have entertainment shows. Casinos often have strict rules about who may play and how much money they can win. Most of them require players to be of legal age to play.

Most modern casinos are large and extravagant buildings designed to impress and delight patrons. Many are located in cities known for their gambling, such as Las Vegas, Nevada; Atlantic City, New Jersey; and Chicago. Casinos are protected by security forces that are trained to detect and deter criminal activity. Modern technology also assists casino security: in some cases, gaming chips have built-in microcircuitry that allows casinos to monitor the amount wagered minute by minute and warn if there is any suspicious or definite deviation from expected results; roulette wheels are electronically monitored with computer systems to reveal quickly any statistical anomalies.

The economic mainstay of most American casinos is the income derived from slot machines and (from the 1980s onwards) video poker. These generate substantial income from small bets made at high speeds on a continuous basis, enabling casinos to achieve mathematical expectancies of profit and control the maximum amounts that can be won by individual patrons. Casinos employ gaming mathematicians and computer programmers to analyze the house edge and variance of casino games, as these factors affect the likelihood that a specific patron will win.