This chapter provides a monumental survey of concepts from a number of disciplines that are relevant to an understanding of improvisation, and outlines a theory of improvisation that concentrates on the psychological bases for moment-to-moment choices within an improvisational structure. The theory is associationistic in nature, and proposes that improvisation proceeds by means of choices of elements which either continue or interrupt some aspect of the immediately preceding context. It deals with the note-by-note structure of an improvisation.