A casino is a building where people can gamble by playing games of chance or skill. The game of choice varies from one casino to another, but there are many popular choices, including blackjack, poker, roulette, craps, and video poker. The house always has a mathematical advantage over the players; this is called the house edge. In games where there is an element of skill, the house may also charge a commission, known as rake, from the players. In addition, casinos may offer free items to their customers, or comps.

Casinos are legal in most states, but vary widely in size and type. The largest are in Nevada and Atlantic City, followed by Iowa. The most popular games are poker, blackjack, and slot machines. The popularity of these games has led to the development of online casinos, which allow players from all over the world to gamble without leaving their homes.

Although gambling probably predates recorded history (carved six-sided dice are found in the earliest archaeological sites), the casino as a place to find all kinds of ways to gamble under one roof did not develop until the 16th century, when a gambling craze swept Europe. In those days, wealthy nobles would hold private parties in their houses, which were called ridotti, to play games like astragali and knucklebones, but they were rarely bothered by authorities. Windows and clocks are rare in casinos, so players can lose track of time and spend hours on the floor without realizing it.