Blackjack Switch is a variant of blackjack in which two hands are dealt to each playing position, and the player is initially allowed to exchange ("switch") the top two cards between hands. For example, if the player is dealt 10-5 and 6-10, then the player may switch to transform the two hands into 10-10 and 6-5. Natural blackjacks are paid 1:1 instead of the standard 3:2, and a dealer hard 22 pushes all player hands except a natural. The initial bets on the two hands must be identical, although during playing out they may be doubled and split independently. The two wagers are resolved separately.

The correct decision regarding whether to switch is sometimes obvious, particularly when there is the largest difference in advantage. However, bordeline and counter-intuitive cases are relatively common, and switching strategy is hard to summarize. While an often-quoted rule of thumb is to choose the option that forms or preserves the best single hand, this is unreliable; sometimes it is even correct to break up a natural by switching, for instance in the case AT + T[3-8] vs. dealer 7, 8 or 9. The correct switching choice depends on the dealer card in a significant minority of cases. Near-optimal schemes which can be learnt have been developed by several authors: Arnold Snyder presents a protocol for switching decisions based on four categories of hand, "winner", "push", "loser" and "chance" [1] which he claims reduces the house edge to 0.25% under his ruleset. Cindy Liu presents a scheme based on assigning a point value to the dealt hands and those produced by switching