The interpretation offered in the present edition is based on an understanding of the hexachordal disposition of Ockeghem’s mass. Since some aspects concerning Missa Quinti toni have not been touched on in the existing literature, the introduction has become quite extensive. After a survey of the sources and their special features, I discuss the relationship between Du Fay’s and Ockeghem’s masses, the questions of Ockeghem’s use of a model, his composing with hexachordal procedures, the use of imitation, and finally his handling of the rhythmic layout of the mass.