Matters of solmization, mode, mensural rhythm and notation, and counterpoint received many theoretical treatments over the course of the fifteenth century, often as part of ardent polemics. The evolution of the music treatise is the objective of this chapter. Several subgenres of the music theory treatise emerged: One can find encyclopedic approaches as well as topic-by-topic organization, and summaries of and commentaries on earlier theoretical traditions as well as cutting edge responses to modern musical practice. Johannes Tinctoris certainly participated in a widespread fifteenth-century tradition of prescriptive responses to current musical practice. The chapter explores how this spectrum of subgenres impacted the treatment of a common set of music-theoretical subjects. To consider this question, the chapter surveys several Italian treatise subgenres, including the encyclopedic summa, the notebook and compendium, the dialogue, the laus musicae, and the focused treatment of notation, counterpoint, and mode. Finally, the chapter concludes by pondering the readership of these theoretical writings.