Blackjack, also known as twenty-one and pontoon in British English , is one of the most popular casino card games in the world. Its precursor was "vingt-et-un" which originated in French casinos around 1700, and which did not offer the 3:2 bonus for a two-card 21. Much of blackjack's popularity is due to the mix of chance with elements of skill and decision making, and the publicity that surrounds the practice of card counting, a skill with which players can turn the odds of the game in their favor by making betting decisions based on the values of the cards known to remain in the deck.

Blackjack hands are scored by their point total. The hand with the highest total wins as long as it doesn't go over 21, which is called a bust. Cards 2 through 10 are worth their face value, and face cards (jack, queen, king) are also worth 10. An ace counts as 11 unless it would bust a hand, in which case it counts as 1.

The goal of each player is to beat the dealer, by having the higher, unbusted hand. Note that if the player busts, he loses, even if the dealer also busts. If the player's and the dealer's hands have the same point value, this is known as a "push", and neither player nor dealer wins the hand.

After initial bets are placed, the dealer deals the cards, either from one or two hand-held decks of cards, known as a "pitch" game, or more commonly from a shoe containing four or more decks. The dealer gives two cards to each player, including himself. One of the dealer's two cards is face-up so all the players can see it, and the other is face down. (The face-down card is known as the "hole card". In European blackjack, the hole card is not actually dealt until the players all play their hands.) The cards are dealt face up from a shoe, or face down if it is a pitch game.

A two-card hand of 21 (an ace plus a ten-value card) is called a "blackjack" or a "natural", and is an automatic winner. A player with a natural is usually paid 3:2 on his bet, although in 2003 some casinos started paying only 6:5 on blackjacks, a move decried by longtime blackjack players.

This is the summary of how the play proceeds after the deal.

* If the dealer has a blackjack and the player doesn't, the dealer wins automatically.
* If the player has a blackjack and the dealer doesn't, the player wins automatically.
* If the player and dealer both have blackjack, it's a tie (push).
* If neither side has a blackjack, then the first player completely plays out his hand, followed by the next player, and so on.
* When all the players have finished the dealer plays his hand.

The player's options for playing his hand are:

* Hit (take another card)
* Stand (take no more cards)
* Double down (double the wager, take exactly one more card, and then stand)
* Split (when the player has identical value cards, such as 8,8, place an additional wager and have each card be the first card in a new hand)
* Surrender (forfeit half his bet and give up his hand. Surrender is not offered at most casinos.)

The player's turn is over after any of the following happens:

* He decides to stand.
* He busts. (in which case he loses even if the dealer subsequently busts, this is the source of the house advantage)
* He doubles down and receives exactly one more card.

After all the players have finished making their decisions, the dealer then reveals the hidden hole card and plays his hand. House rules say that the dealer must hit until he has at least 17, regardless of what the players have. In most casinos a dealer must also hit a soft 17 (such as an Ace and a 6). The table felt will indicate whether the dealer hits or stands on soft 17.

If the dealer busts then all remaining players win. Bets are normally paid out at the odds of 1:1.

Some common rules variations

* one card split aces: one card is dealt on each ace, players turn is over.
* early surrender: player has the option to surrender before dealer checks for BlackJack.
* late surrender: player has the option to surrender after dealer checks for BlackJack.
* double-down restrictions: double-down allowed only on certain combinations.

There are more than a few blackjack variations which can be found in the casinos, each has its own set of rules, strategies and odds. it is advised to take a look at the blackjack rules of the specific variation before playing.