The number of decks in play significantly impacts Blackjack by altering the probabilities and strategies involved. With fewer decks, the composition of the remaining cards is more predictable, making it easier for players to gauge the likelihood of drawing high or low cards, which can lower the house edge. In contrast, using more decks dilutes these probabilities and increases the house edge, making the game slightly less favorable for players. This also affects basic strategy, as certain decisions—like when to hit or stand—can change based on the number of decks in use. Additionally, card counting becomes more difficult with multiple decks because it's harder to track the deck’s composition, reducing the effectiveness of that strategy. Overall, single-deck games offer a slight edge to players compared to multi-deck games due to the more concentrated card composition and higher frequency of favorable outcomes.