The purpose of this study was to create and validate a measure for jazz theory knowledge assessment. The Jazz Theory Measure (JTM) was created by exploring publications on jazz improvisation instruction and research studies that utilized jazz theory as a significant aspect of the study (i.e., dependent variable, independent variable, data collection). Latent jazz theory components (i.e., Key Knowledge, Scale Knowledge, and Chord Knowledge) were identified from an exploration of the literature and each was paired with several subtests. Items representing the JTM (N = 60) demonstrate significant representation of the jazz theory components through alpha reliability (0.98), and confirmatory factor analysis (standardized root mean square residual [SRMR] = 0.0327, comparative fit index [CFI] = 0.930, Tucker-Lewis index [TLI] = 0.907) providing support for the JTM as a valid and reliable measure of jazz theory knowledge. Further analysis suggests that music educators providing instruction in jazz improvisation should focus on building a foundation of jazz theory in the first 5 years of jazz instruction.