Johannes de Grocheio is best known today primarily for the fact that he wrote about secular monophony, a subject practically ignored by previous music writers. In Grocheio’s only surviving treatise, which modern scholarship has christened De musica (it is actually untitled in the manuscripts), he provides an unparalleled witness to Parisian musical life around 1300 through a wide-ranging classification of musical performances. The treatise’s tantalisingly realistic observations have been by far the most discussed aspect of De musica in over a century of modern scholarship ranging from an early landmark critical edition to recent postmodern readings. However, for those intent on discovering thirteenth-century performance practice, Grocheio has been as much a musicological frustration as a delight. The most egregious problem is that he appears not to describe some of his musical examples accurately. What has been lost in a great deal of this discussion is the extent to which Grocheio’s unique perspective shapes his discussion of music.