Interaction is an integral part of all music. Interaction is part of listening, of playing, of composing and even of thinking about music. In this book the multiplicity of modes in which one may engage interactively in, through and with music is the starting-point for rethinking human-computer interaction in general and interactive music in particular. It is proposed that in human-computer interaction the methodology of control (interaction-as-control) in certain cases should be abandoned in favour of a more dynamic and reciprocal mode of interaction (interaction-as-difference): interaction as an activity concerned with inducing differences that make a difference. Interaction-as-difference suggests a kind of parallelism rather than click-and response. In essence, the movement from control to difference is a result of rediscovering the power of improvisation as a method for organising and constructing musical content. The notion of the giving up of the Self is furthermore suggested as the prerequisite for an improvisatory and self-organising attitude towards musical practice that allows for interaction-as-difference.