""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."