A casino (also spelled casin) is a room or building in which gambling games are played. In the United States, a casino is usually a public building that houses gambling tables, slot machines, and other gambling equipment. It is also a place where patrons may gamble and socialize. Casinos are most often located in cities with substantial tourist populations, such as Las Vegas and Atlantic City.

In the 21st century, the number of casinos has grown rapidly. In the United States, over 40 states now have casinos. Casinos have become a significant driver of regional economic development, and many communities have gained wealth by becoming centers for casino-based gambling. However, the large amount of money handled in casinos makes them susceptible to cheating and theft, both from patrons and staff. Therefore, most casinos have security measures to prevent these crimes.

Most casinos offer traditional card and dice games such as baccarat, chemin de fer, blackjack, and poker. In addition, some casinos specialize in far Eastern games such as sic bo (which has spread from London clubs to most European and American casinos), fan-tan, and pai gow.

Many modern casinos rely on the statistical analysis of games to make profits. This requires specialized mathematicians and computer programmers to develop mathematically optimal plays for various casino games, including those with a skill element, such as blackjack. Casinos use this information to calculate the house edge and variance for each game and to determine how much money to keep in reserve.