A multi-user system, for interactively controlling the action of at least a first participant in an environment, comprising: a first device operable by a first user to dynamically control the action of the first participant in the environment; and a second device simultaneously operable by a second user to dynamically vary the environment. A method for multi-user interactive control of at least a first participant in an environment, comprising the steps: a first user dynamically controls the action of the first participant in the environment; and simultaneously, a second user dynamically varies the environment. Described embodiments include a musical environment in which the participant is a musical instrument and a gaming environment in which the participant is a character in a game.