No specific compositions are attributed to Léonin, but Anonymous IV gives him credit for creating the Magnus Liber (Great Book) of Organum.
Several musicologist such as Craig Wright have suggested that the composer Léonin is also the contemporary Parisian poet, Leonius.
Léonin and Anonymous IVEdit
Little is know about the music treatise of Anonymous IV, and even less so about Léonin himself, but surviving copies of the treatise do give an insight into Léonin's role in developing the Notre Dame school of polyphony.
"These rules are used in many books of the antiqui, and this from the time of the great Perotinus, … and likewise from the time of Leo, for his part … And note that Magister Leoninus, so it has been said, was the best worker with organum [optimus organista] who made [‘fecit’] the great book of polyphony [magnus liber organi] on the gradual and antiphonary to embellish the divine service. This was in use up to the time of the great Perotinus, who made a redaction of it [‘abbreviavit eundem’] and made many better clausulas, or puncta, he being the best worker with discant [‘discantor’], and better [at discant] than Leoninus was. But the same cannot be said regarding the subtlety of organum [purum], etc.” (treatise of Anonymous IV)
While there were collections of notated organum that date to before the time of the Magnus Liber, the Liber stands out for a few reasons. Several early extant copies can still be studied by current musicologists which makes the Liber more applicable to current research. Also, the Liber contains numerous examples of melismatic clausulae, as well as extended two part organum (organum duplum). This allows scholars to trace the development of organum and plainchant from it's early improvised days in the 9th and 10th centuries to the beginnings of a codified system of notation and compositional rules found in the late 12th century.
Hiley, David. "Léonin." The Oxford Companion to Music. Oxford Music Online. Oxford University Press, accessed January 18, 2014, http://www.oxfordmusiconline.com/subscriber/article/opr/t114/e3934.
Edward H. Roesner. "Leoninus." Grove Music Online. Oxford Music Online. Oxford University Press, accessed January 18, 2014, http://www.oxfordmusiconline.com/subscriber/article/grove/music/40466.