The music in the Eton Choirbook presents a we:tlth of information regarding late fifteenth-century English compositional practice which until now has received little close attention. This study explores aspects of compositional practice through analysis of cantus firmus procedures within the Choirbook. The use of a cantus firmus in the Eton Choirbook is investigated in the works of the most prolific (and perhaps creative) composer, John Browne, in the $Salve\; regina$ settings and in the $Magnificat$ settings.

The study has been enriched by the discovery of the identity of four cantus firmi in compositions by Banester, Davy, Wylkynson and Browne. In addition, a new source for coumerpoints to the $Magnifical$ tones has been documented.

John Browne incorporates a $cantus\; firmus$ into each of his compositions. His selection and treatment of $cantus\; firmus$ demonsrrate that he was a composer of considerable versatility, who experimented with a variety of ways of including a cantus firmus. The skill with which he integrates a cantus finnus, matching similar ideas in set text and unheard cantus firmus text suggests an additional personal dimension to the choice and treatment of the cantus firmus. The links between cantus firmus and set text are considered further in a discursus on Banester's $O\; Maria\; et\; Elizabeth.$

The employment of a $cantus\; firmus$ as a means of defining the structure as well as clarifying the sense of a text is investigated further in the Eton $Salve\; regina$ settings. The identification of the cantus finnus in Wylkynson's setting of $O\; virgo\; prudentissima$ is considered in the light of the choice and treatment of cantus firmus in both this piece and his nine-voice $Salve\; regina$ and suggests that Wylkynson's personal religious consciousness involved a devotion to angels.

The inclusion of a pre-existent melody is explored further in the Eton $Magnificat$ settings. Most of the $Magnificat$ settings incorporate a pre-existent counterpoint to one of the $Magnificat$ tones as a type of $cantus\; firmus.$ An examination of three sources for such $Magnificat$ counterpoints includes discussion of one source that has been discovered only recently.

Critical analyses of compositions in the Choirbook reveal that the presence of a cantus firmus seems to be used to articulate the sense of and reinforce the impact of ideas in the set text in a number of the Eton compositions. This offers a new theoretical perspective to the understanding of the manner in which a cantus firmus may be incorporated in late fifteenth-century English music.

The Appendices include editions of ten unpublished fragmentary compositions in the Eton Choirbook and transcriptions of the three principal sources for the mensural counterpoints to the $Magnificat$ tones.