Doubling down in blackjack allows players to double their original bet after receiving their first two cards, in exchange for committing to stand after receiving one additional card. This option is typically available when the player's total is 10 or 11, giving them a favorable chance to improve their hand. Some casinos may allow doubling down on other totals, such as 9 or even after splitting pairs. Players must follow specific house rules regarding when and how they can double down, and they usually cannot double down after taking additional cards.