Along with Johannes de Garlandia and Franco of Cologne, whose work precedes his, Anonymous IV's writings are the main source for understanding the Notre Dame school of polyphony.
He wrote about Léonin and Pérotin, thereby assigning names to two of the composers of the music of the Notre Dame school who otherwise would have been anonymous.
He also mentions specific compositions as being by Pérotin (or Perotinus), including the four-part organa quadrupla Viderunt and Sederunt.
Anonymous IV also mentions the work of the theorist Franco of Cologne; describes organum, discantus, rhythmic modes, and genres of composition; and gives rules for the use of notation and of consonance and dissonance.
Although the older translation by Luther Dittmer has long been unavailable, it has recently been released online by the Institute of Medieval Music.