 His most famous composition is a complete setting of the mass, for three voices, which contains some of the earliest use of fauxbourdon.An unusual feature of this mass is that it contains music not only for the Ordinary (Kyrie, Gloria, Credo, Sanctus, Agnus Dei) but the Proper as well; in this regard it resembles the "Missa Sancti Jacobi" of Guillaume Dufay, which is often considered to be the earliest example of fauxbourdon to which the term was applied by the composer.Libert's mass uses a plainsong source which permeates all the movements, and migrates from voice to voice.