The first volume of the thesis consists of five chapters and five appendices. The first, biographical, chapter outlines the evidence of the composer's life to be found in contemporary seventeenth century writings and in surviving MSS of his music. The second chapter examines more closely the evidence of the MS sources in relation to the chronology of Jenkins' music and contains a reassessment of his output in the light of this evidence. In the third chapter the hundred or so MSS are critically examined and classified according to their merit as authoritative sources of Jenkins' works; the question of the composer's autograph and those of a few of his associates is discussed in some detail with photographic illustrations. The fourth chapter provides an illustrated outline of the evidence found in these MSS of the performing practice and instrumentation in Jenkins' music with some valuable new material on the English "graces" for the bass viol. The fifth chapter provides a survey of Jenkins' use of the forms current in England during his lifetime. His music is related as far as possible to that of his predecessors and contemporaries and attention is paid to those works in which a division texture is superimposed on fantasia or dance forms. The five appendices are: a checklist of all known sources, including modern editions, of Jenkins' instrumental music; a descriptive catalogue of the MS sources; a list of his vocal works, by first lines; a bibliography of contemporary publications of instrumental and vocal music up to 1680; and a select general bibliography.