Blackjack is a card game where the goal is to get as close as possible to 21 without going bust. Players are dealt two cards and can decide whether to stand, hit, double down or surrender (if allowed). The dealer also receives two cards.

The player’s decision can be influenced by the value of their cards, the dealer’s position and other factors. A knowledge of basic strategy and the house edge can help players to make informed choices.

Card values in blackjack are based on the number of each card, as well as its suit and face value. Number cards are worth their number, face cards are worth 10 and aces are worth one or 11. The aim of the game is to build a hand with a value higher than the dealer’s.

Players bet against the dealer and win when their hand totals higher than the dealer’s or they have 21. The dealer loses if they go bust or their hand is worth less than 21.

The basic strategy for blackjack was devised by four US army engineers in the 1950s. It has been refined over the years, using computers to simulate millions of blackjack hands. This has led to a mathematically sound strategy that gives the player a better chance of winning.

A key point in the basic strategy is that a hard hand must always be played differently from a soft one. For example, if a player has a 6 and an 8, they should split the cards and play them as two separate hands. This will eliminate the possibility of a bust, and in the case of 8s, it will give the player the option to hit.

Doubling down in blackjack is an option when a player has two matching cards, such as two sevens or two threes. This is done by placing a second bet alongside the original one and playing the cards as if they were two separate hands. It can be profitable in some situations, but the key is to know when to do it and how much to bet on each hand.

Other variations on blackjack include side bets, which allow players to place additional wagers on various outcomes of the dealer’s hand. This can be useful in reducing the house edge and making the game more exciting.

Some players will also learn to count cards in blackjack, which can improve their odds of winning. This involves keeping a running total of the cards as they are dealt and increasing your bets when the count is in your favor. This is a challenging skill to master, but can lead to significant returns. Casinos are wise to card counters, so they will often switch to a single-deck shoe when the count is high. A true count takes the running total and multiplies it by the number of decks being used, to give a more accurate picture of the dealer’s advantage.