GenJam is an interactive genetic algorithm (GA) that models a human jazz improviser and performs regularly as the author's sideman on jazz gigs. GenJam learns to improvise full-chorus solos under the guidance of a human mentor and “trades fours” in real time with a human performer in “chase” choruses. In this article, the author first briefly describes GenJam's architecture, representations, genetic operators and performance characteristics. He then places GenJam in the context of a proposed taxonomy for GA-based music and art systems.