The purpose of this exploratory study was to examine the role aural imitation ability, jazz theory knowledge, and personal background variables play in the development of jazz improvisation achievement. Participants (N = 70) included 26 high school and 44 college instrumentalists with varying degrees of jazz improvisation experience. Data were collected using four researcher-designed instruments: (a) Participant Improvisation Experience Survey (PIES), (b) Improvisation Achievement Performance Measure (IAPM), (c) Aural Imitation Measure (AIM), and (d) the Jazz Theory Measure (JTM). Results indicate that aural imitation ability and technical facility are fundamental skills supporting jazz improvisation achievement. Other contributing factors include improvisation experience, jazz experience, practicing improvisation, perceived self-confidence, self-assessment, and jazz theory knowledge. Further analysis of results led to improvisation being viewed from a developmental perspective and achievement levels being distinguished on a developmental continuum (i.e., novice, intermediate, advanced) based on performance evaluations within musical categories (i.e., rhythm/time feel, harmony, melody/rhythmic development, style, expressivity, and creativity).