Blackjack, also known as Twenty-one or Vingt-et-un (French for "twenty-one"), is a comparing-type card game which is the most widely played casino banking game in the world. The standard game is played with one or more French decks of 52 cards. The player draws cards to an initial two card hand with the object of bringing the total hand value as close as possible to 21 without exceeding it, so that the house, which plays after the player, will fail to get up to the player's total, or will lose by exceeding 21.

 Blackjack is played in many variations at casinos with different table rules. Much of blackjack's popularity is due to the mix of chance, skill, and the publicity that surrounds card counting, which entails adapting one's wager and playing strategy to the profile of cards yet to be dealt. Blackjack is closely related to the games of Spanish 21 and Pontoon, but unrelated to the British game with the similar name Black Jack which is a shedding-type card game.

In blackjack at a casino, the dealer faces between five and nine (commonly seven) playing positions from behind a semicircular table. Each position may be occupied by up to three players. A single player is often permitted to control or bet on as many positions as desired. At the beginning of each round, bets are placed in the "betting box" at each position in play.

The player whose bet is at the front of the betting box is deemed to have control over the position, and the dealer will consult the controlling player for playing decisions regarding the hand. Each wagered-on position is dealt an initial hand of two cards visible to the player of that box, and often to any other players. The dealer receives a single face up card, and in some games draws a second card, concealed from the players (the "hole" card, used to establish immediately whether the dealer has blackjack).

Hole card games ares sometimes played on tables with a small mirror or electronic sensor which the dealer can use to check the hole card's exact denomination, without revealing it if it does not result in blackjack. In European casinos, no hole card games are prevalent; the dealer's second card is neither drawn nor consulted until the players have all played their hands.

Cards are dealt either from one or two hand-held decks, from a dealer's shoe, or from a shuffling machine. Single cards are dealt to each of wagered-on position clockwise from the dealer's leftmost position, followed by a single card to the dealer, followed by an additional card to each of the positions in play.