This article maps out some of the relationships between performers and their instruments in live and improvised electronic music. In these practices, musical machines – be they computers, mechanical assemblages or combinations of different sound-makers and processors – act as generators of musical material and sources of unpredictability with which to improvise. As a lens through which to consider these practices, we examine a number of different roles these musical machines may take on during improvised performances. These include running, playing, surprising, evolving, malfunctioning, collaborating and learning. We explore the values of these different roles to the improvising musician, and contextualise them within some broad and historical trends of contemporary music. Finally, we consider how this taxonomy may make us more open to the vital materialism of musical instruments, and offer novel insights into the flows of agency and interaction possibilities in technologically mediated musical practices.