Casinos have specific regulations regarding card counting in blackjack, though card counting itself is not illegal. Casinos consider it a form of advantage play, and they may take measures to deter or prevent it. This can include observing players for suspicious betting patterns, limiting the number of decks used, using automatic shuffling machines, or even banning players they suspect of counting cards. While players can technically count cards, they must do so discreetly and be aware that casinos have the right to refuse service to anyone they believe is gaining an unfair advantage.