KYKLOS, an algorithmic composition program, is presented here. Itgeneralises musical scales for use in composition as well as inperformance. The sonic output of the system is referred to aspolymodal music since it consists of four independent voicesplaying ‘synthetic modes’. KYKLOS is suitable forcomputer-assisted composition because it generates MIDI files which can bealtered later by the composer. It can equally well be used in liveperformance for dynamic modification of parameters enabling realtimemusical control.