Counting cards is not illegal, but casinos generally disapprove of the practice and may take measures to prevent it. Card counting is a strategy used in games like blackjack to gain an advantage by tracking the ratio of high to low cards remaining in the deck. While players have the right to use their skills and memory, casinos can refuse service or bar players they suspect of counting cards. As a result, while there are no legal restrictions against the practice itself, the consequences from the casino can impact a player's future participation.