This edition, for the first time, presents a complete modern rendering of an extensive repertoire of works crucial to the development of polyphonic Western music, the organa at Notre Dame cathedral of Paris ca.1165-1225. The two chief composers, Leonin and Perotin, devised the first musical notation to indicate pitch and rhythm, and formulated several musical styles and types of composition which were sung throughout Europe for approximately two centuries. Hans Tischler's edition explores the evolution of compositional methods for both composers, examining the individual styles of organum purum, discant, copula, and pseudo-discant. A second evolutionary factor considered is the selected use of melodic formulae and the recurrence of whole phrases and sections which interrelate numerous organa. A third consideration of the analysis is the increasing complexity of the rhythmic treatment in the tenors of discant clausulae, from Leonin's creation of modal notation, to Perotin's invention of additional rhythmic patterns and their notational symbols. The repertoire comprises settings of well over one hundred chants, the majority of them in two or three versions; and each setting is comprised of several independent and exchangeable sections, totaling approximately 1,500. Only portions of this vast repertoire have been previously published, however, this edition includes all relevant extant material, drawn from sixteen manuscripts, several of which contain two or more collections of organal works . It also refers to related compositions in seven additional collections and to chant sources in eight medieval and eight modem codices.