Recent research on the library of Johann Caspar Trost the Elder, organist in Halberstadt, has led to the identification of a manuscript with two unknown treatises on musica poetica, one a lost treatise by Johann Hermann Schein and the other an unknown treatise by Michael Altenburg. Together they offer fresh insights into the learning and teaching of music in the early modern period. The books once owned by Trost also have close connections to his personal and professional life. This article situates the newly discovered manuscript in the framework of book history and Trost’s biography, and discusses the two treatises against the background of contemporary books of musical instruction (Calvisius, Lippius, or Finolt). The historical context of the manuscript, its theoretical sources and its origins all serve to contribute to and further the current understanding of musical education in early modern central Germany. An edition of the treatises is provided.