In Professor Pac-Man, players must answer multiple-choice questions by using the buttons on the control panel. Unusually for an arcade game, the first player's buttons are on the right side of the panel, while the second player's are on the left side.
In a 1-player game, the Professor challenges the player to answer his questions correctly and quickly in order to get the highest score. The player is given two chances to answer each question - but if he answers incorrectly on the first time, he will lose a life. If time still remains on the question, he can try to answer it again - however, if the time runs out before he has the chance to do so, he will not lose another life. But if he does have enough time to try and answer the question again and is still incorrect, he will lose another life. The player can use this to his advantage by not trying to answer a question for the second time if he is not entirely sure of the answer, as he will not lose another life if he does not try - but he will lose a life for a second attempt which turns out to be incorrect. Bonus questions are awarded if the player answers a certain number of questions correctly without any mistakes - and if the player answers one correctly, he will receive an extra life and twice the usual point value. The player is only given one chance to answer a bonus question correctly, though - but if he answers one incorrectly, he will not lose a life. Once the player runs out of lives, his game is over and he must watch the Professor waving goodbye while the moon is setting in the background.
In a 2-player game, the players compete against each other, to see who can get the correct answer first for each question. The player who manages to do this will receive the points for the question - but if one of the players answers a question incorrectly, he will lose a life and the other player must try to answer correctly in the time remaining. If he either fails to answer or answers incorrectly, he will also lose a life. When one player runs out of lives, his game is over and the other player continues from the current point as if it was a 1-player game (that is, he is given two chances to answer each question). Once the other player runs out of lives, his game is also over and once again, he must also watch the Professor waving goodbye.