Interactivity refers broadly to human-computer musical interaction, or human-human musical interaction that is mediated through a computer, or possibly a series of networked computers that are also interacting with each other. Often, an interactive performance, composition or improvisation will involve the creation or programming of software that will respond to pre-determined aspects of a live performance. The software will then determine other aspects of the music, either generating synthesised sound, or modifying in some way all or some of the 'live' sound.
The behaviour of the computer may be highly determined or indeterminate as defined by the musicians, and may be modified from performance to performance. The exact musical role of the computer may even be modified in real-time during the course of a performance.
Interactive music-making introduces and often utilises notions of virtual instrument, virtual performer, virtual composer, and even virtual listener.
Interactive music-making frequently blurs the conventional distinction between compositional and improvisational activity. Key issues in interactive music making are socialisation, collective authorship, geographical and temporal synchronicity/asynchronicity, and 'distributed activity'.