The game unit has four large buttons, one each of the colors red, blue, green, and yellow. The unit lights these buttons in a sequence, playing a tone for each button; the player must press the buttons in the same sequence. The sequence begins with a single button chosen randomly, and adds another randomly-chosen button to the end of the sequence each time the player follows it successfully. Gameplay ends when the player makes a mistake or when the player wins (by matching the pattern for a predetermined number of tones).
Simon was later re-released by Milton Bradley (now owned by Hasbro), in its original circular form, though with a translucent case rather than plain black. It was also sold as a two-sided "Simon Squared" version, with the reverse side having eight buttons for head-to-head play, and as keychain (officially licensed by Fun4All) with simplified game play (only having Game 1, Difficulty 4 available). Other variations of the original game, no longer produced, include Pocket Simon and the eight-button Super Simon, both from 1980.