Card counting in blackjack is a strategy that involves tracking the ratio of high to low cards remaining in the deck to assess the player's advantage. Players assign values to cards, maintaining a running count based on these values. A higher positive count indicates a greater proportion of high cards, leading players to increase their bets. Many also convert the running count into a true count, adjusting for the number of decks. While it can provide a strategic advantage, successful card counting requires practice, focus, and careful execution in a casino environment.