Composing and improvising are contrasting yet highly complementary modes of musical expression. Both are capable of standing on their own as rich forms of creativity. Improvisation uniquely enables a kind of real-time, spontaneous invention and interaction that is not possible through the discontinuous temporality of composition, where pieces are melded over a series of creative episodes that may span weeks or months. On the other hand, the very discontinuous temporal framework of composition is uniquely suited to another kind of expressive result-the design of rich formal architectures. As the saxophonist Steve Lacy remarked, “there is a music that must be composed, there is another music that can only be improvised.”1