It uses decks of 52 cards and descends from a global family of casino banking games known as "twenty-one".

Blackjack's immediate precursor was the English version of twenty-one called vingt-un, a game of unknown provenance.

The first written reference is found in a book by the Spanish author Miguel de Cervantes.

Cervantes was a gambler, and the protagonists of his "Rinconete y Cortadillo", from Novelas Ejemplares, are card cheats in Seville.

They are proficient at cheating at veintiuno (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.

"Rinconete y Cortadillo" was written between 1601 and 1602, implying that ventiuno was played in Castile since the beginning of the 17th century or earlier.

[4] According to popular myth, when vingt-un was introduced into the United States (in the early 1800s, during the First World War, or in the 1930s, depending on the source), gambling houses offered bonus payouts to stimulate players' interests.

He could not find any historical evidence for a special bonus for having the combination of an ace and a black jack.

[4] 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,[9] the first mathematically sound optimal blackjack strategy.

Ed Thorp used Baldwin's hand calculations to verify the basic strategy and later published (in 1963) Beat the Dealer.

The players' initial cards may be dealt face-up or face-down (more common in single and double-deck games).

In handheld games, a player must reveal their cards if they have a blackjack, bust, or wish to double down, split, or surrender.

Hand signals help the "eye in the sky" make a video recording of the table, which resolves disputes and identifies dealer mistakes.

In some games, players can also take insurance when a 10-valued card shows, but the dealer has an ace in the hole less than one-tenth of the time.

Each game has a rule about whether the dealer must hit or stand on soft 17, which is generally printed on the table surface.

[13] Casinos generally compensate by tightening other rules in games with fewer decks, to preserve the house edge or discourage play altogether.

The following table illustrates the mathematical effect on the house edge of the number of decks, by considering games with various deck counts under the following ruleset: double after split allowed, resplit to four hands allowed, no hitting split aces, no surrendering, double on any two cards, original bets only lost on dealer blackjack, dealer hits soft 17, and cut-card used.

Note that a ten-value card dealt on a split ace (or vice versa) will not be counted as a blackjack but as a soft 21.

"Original bets only" is also known by the acronym OBO; it has the same effect on basic strategy and the house edge as reverting to a hole card game.

Among common rule variations in the U.S., these altered payouts for blackjack are the most damaging to the player, causing the greatest increase in house edge.

When using basic strategy, the long-term house advantage (the expected loss of the player) is minimized.

Regardless of the specific rule variations, taking insurance or "even money" is never the correct play under a basic strategy.

Casino promotions such as complimentary matchplay vouchers or 2:1 blackjack payouts allow players to acquire an advantage without deviating from basic strategy.

Card counting is legal,[21]: 6–7  but a casino might inform counters that they are no longer welcome to play blackjack.

[23] Arnold Snyder's articles in Blackjack Forum magazine brought shuffle tracking to the general public.

Only a few side bets, like "Insurance" and "Lucky Ladies", correlate well with the high-low counting system and offer a sufficient win rate to justify the effort of advantage play.

Some casinos, as well as general betting outlets, provide blackjack among a selection of casino-style games at electronic consoles.

[29] Blackjack is a member of the family of traditional card games played recreationally worldwide.

Examples of local traditional and recreational related games include French vingt-et-un ('twenty-one') and German Siebzehn und Vier ('seventeen and four').

The popular British member of the vingt-un family is called "pontoon", the name being probably a corruption of vingt-et-un.