In Blackjack, casinos shuffle decks using a combination of manual and machine methods to ensure fairness, prevent cheating, and maintain the integrity of the game. Dealers may manually shuffle the cards, especially with fewer decks, by splitting and mixing the piles, often followed by a "cut" performed by a player. For games with multiple decks, automatic shuffling machines are used to shuffle quickly and efficiently, reducing human error. Some casinos also use continuous shuffling machines that keep the cards in constant rotation, making it harder for players to track or count cards. Overall, these methods are designed to ensure randomness and security, making it difficult for players to gain an unfair advantage.