Simon says is a game for three or more players (most often children). One of the people is "it" – i.e., Simon. The others must do what Simon tells them to do when asked with a phrase beginning with "Simon says". If Simon says "Simon says jump", the players must jump (players that do not jump are out). However, if Simon says simply "jump", without first saying "Simon says", players do not jump; those that do jump are out. In general, it is the spirit of the command, not the actions that matters; if Simon says "Simon says touch your toes", players only have to show that they are trying to touch their toes. It is the ability to distinguish between valid and invalid commands, rather than physical ability, that matters here.

It is Simon's task to try to get everyone out as quickly as possible, and it is every one else's job to stay "in" for as long as possible. The last of Simon's followers to stay in wins (although the game is not always played all the way through).

It is considered cheating to give impossible commands ("Simon says 'lift both of your legs up and keep them there!'.") or phrase the commands in such a way that the other player has no option but to 'go out' ("Simon says 'jump up'. Come down."). However, at least in some versions, it is allowed for Simon to eliminate players by asking them to do something seemingly unrelated to the game (example: "Anyone remaining join me up here.").