Writing in 1970 of Robert Simpson's music, Hugh Ottaway said, "Simpson's ideal is a Beethovenian dynamism and comprehensiveness, an active unity in which powerful forces are embraced and subdued: a sense of re-engagement with the humanist mainstream, clear-headed and unsentimental is implicit in everything he writes." Simpson's dogged musical integrity has resulted in a high degree of consistency and homogeneity in his compositional development. But in the thirty-seven years that he has been writing symphonies his approach to the ideals mentioned by Ottaway has deepened in strength and subtlety and his achievement has steadily increased in breadth and power. This dissertation traces his development as a symphonist. The discussion of Symphonies 1-3 demonstrates how their dynamic approach to tonality is expressed in terms of sustained keyconflict. Particularly close attention is given to the Third Symphony - probably the finest of the three. From the early 1970s onwards a change is detectable in the way In which Simpson organises his music. Emphasis upon keyconflict gives way to a concern with the generative powers of certain intervals and the analyses of the symphonies from No.4 onwards reflect the increasing concentration with which Simpson derives his material from a small group of intervals. The analytical approach to each work is essentially a narrative one in keeping with the organic manner in which Simpson's music grows. The dissertation ends with a brief commentary upon Symphony No.10 which, at the time of writing has only just been completed and remains unperformed.