The medieval office of the dead has received only passing mention in studies of Western plainchant. Its rapid diffusion and increase in practical use throughout Europe is a consequence of priorities in worship at the Abbey of Cluny and the introduction of All Souls' Day to the Christian calendar. Gabriel Beyssac investigated the Cluny office of the dead, but his results were not published. Only Knud Ottosen, a professor of theology at the University of Aarhus, has described it within a book on the responsory and verse texts for known Western offices of the dead, which does not consider the music. The place of the office of the dead in the liturgy of Cluny will be discussed. The musical structure of the office and its melodies will be identified. An edition of the office from the manuscript breviary, Solesmes (Sarthe), Abbaye Saint-Pierre, Bibliothèque, Réserve, Ms. 334, concludes the thesis.