My research project concerns the encyclopedic treatise on music written by Ugolino of Orvieto (ca. 1380–1452), a composer, music theorist, and archpriest of the Cathedral of Ferrara. His summa on all aspects of musical learning situates ancient and medieval writers alongside his contemporary commentators. Celebrated in his own day as one who would surpass all other musicians, Ugolino bridged a long-established divide between abstract, speculative musical thought about the harmony of the spheres and the practicalities of musical notation, composition, and singing. During my time at the American Academy in Rome, I will complete a new and more accessible edition, first-ever translation, and monographic study of Ugolino’s Declaratio musice discipline. My edition proposes new readings of the text based on a close reexamination of the fifteen manuscript sources, including three major sources held in Roman libraries, as well as the treatise’s many unacknowledged intertextual references.