Blackjack, also known as twenty-one, is a comparing card game between usually several players and a dealer, where each player in turn competes against the dealer, but players do not play against each other. It is played with one or more decks of 52 cards, and is the most widely played casino banking game in the world.
Blackjack's precursor was twenty-one, a game of unknown origin. The first written reference is found in a book by the Spanish author Miguel de Cervantes, most famous for writing Don Quixote. Cervantes was a gambler, and the main characters of his tale "Rinconete y Cortadillo", from Novelas Ejemplares, are a couple of cheats working in Seville. They are proficient at cheating at veintiuna (Spanish for twenty-one), and state that the object of the game is to reach 21 points without going over and that the ace values 1 or 11. The game is played with the Spanish baraja deck, which lacks eights and nines. This short story was written between 1601 and 1602, implying that ventiuna was played in Castile since the beginning of the 17th century or earlier. Later references to this game are found in France and Spain.
When twenty-one was introduced in the United States, gambling houses offered bonus payouts to stimulate players' interest. One such bonus was a ten-to-one payout if the player's hand consisted of the ace of spades and a black jack (either thejack of clubs or the jack of spades). This hand was called a "blackjack", and the name stuck to the game even though the ten-to-one bonus was soon withdrawn. In the modern game, a blackjack refers to any hand of an ace plus a ten or face card regardless of suits or colours.
The first scientific and mathematically sound attempt to devise an optimal blackjack playing strategy was revealed in September 1956. Roger Baldwin, Wilbert Cantey, Herbert Maisel and James McDermott published a paper titled The Optimum Strategy in Blackjack in the Journal of the American Statistical Association. This paper would become the foundation of all future sound efforts to beat the game of blackjack. Ed Thorp would use Baldwin’s hand calculations to verify the basic strategy and later publish (in 1963) his famous book Beat the Dealer.
Players are each dealt two cards, face up or down depending on the casino and the table at which you sit. In the U.S., the dealer is also dealt two cards, normally one up (exposed) and one down hidden). In most other countries, the dealer receives one card face up. The value of cards two through ten is their pip value (2 through 10). Face cards (Jack, Queen, and King) are all worth ten. Aces can be worth one or eleven. A hand's value is the sum of the card values. Players are allowed to draw additional cards to improve their hands. A hand with an ace valued as 11 is called "soft", meaning that the hand will not bust by taking an additional card; the value of the ace will become one to prevent the hand from exceeding 21. Otherwise, the hand is "hard".
Once all the players have completed their hands, it is the dealer’s turn. The dealer hand will not be completed if all players have either busted or received Blackjacks. The dealer then reveals the hidden card and must hit until the cards total 17 or more points. (At most tables the dealer also hits on a "soft" 17, i.e. a hand containing an ace and one or more other cards totaling six.) Players win by not busting and having a total higher than the dealer, or not busting and having the dealer bust, or getting a blackjack without the dealer getting a blackjack. If the player and dealer have the same total (not counting blackjacks), this is called a "push", and the player typically does not win or lose money on that hand. Otherwise, the dealer wins.
Blackjack has many rule variations. Since the 1960s, blackjack has been a high-profile target of advantage players, particularly card counters, who track the profile of cards that have been dealt and adapt their wagers and playing strategies accordingly.
Blackjack has inspired other casino games, including Spanish 21 and pontoon.