In this chapter, the authors talk about the former: programming bespoke musician logic. After learning how to assemble musical logic in this way, it should be straightforward to port these techniques to a modular system. Composers are everywhere—in pop music, classical music, game music, electronic dance music, and more. Composers create a piece of music for a set of musicians and usually record a performance. Music improvisation is the embellishment of musical ideas. Those ideas can come from a composer, other musicians, or several musical “games” used to generate the basis for the improvisation. Most interactive music systems require something to tell time or to send a signal when a musical interval is encountered. Jazz music provides a useful framework for autonomous music, thanks to its focus on improvisation and well-defined theory. Leaning on the composer, musician, instrument metaphor further grounds the concept such that we can visualize how the code components come together.