In the Christian West, rituals surrounding death were characterized musically, until the mid fifteenth century, exclusively by plainchant. However, from the mid fifteenth century on, composers began to set the Mass of the Dead in polyphony. The polyphonic Requiem was a watershed departure, yet it continued to use the traditional plainchant as its starting point and structural governor. Understanding this plainchant starting point is thus essential for understanding the early polyphonic Requiem. However, fifteenth- and sixteenth century chant traditions are currently little understood: in the fifteenth and sixteenth centuries, chant was not a uniform, stable repertory, but subject to more or less extreme regional variation, in matters ranging from melodic detail to overall structure. This project will research these variants not only to illuminate late-medieval and Renaissance chant traditions in themselves, but also to provide a basis for contextualizing and analyzing the early polyphonic Requiem.