Card counting in blackjack involves tracking the ratio of high cards (10s, face cards, Aces) to low cards (2-6) remaining in the deck. By assigning values to the cards—high cards as negative, low cards as positive, and neutral cards as zero—you maintain a running count. As cards are dealt, you adjust the count accordingly. To account for multiple decks, you convert the running count into a "true count" by dividing it by the number of decks remaining. When the true count is positive, it indicates an advantage for the player, prompting you to increase your bets. When the count is negative or neutral, you should bet conservatively. To avoid detection, good card counters vary their bets subtly and play casually, as casinos can ask players to leave if they suspect card counting.