This dissertation comprises a study of the composer Toru Takemitsu, vis-a-vis his creative sources, for example, those extra-musical influences that inspire his compositions. The work is organized into the following categories: (1) his early years, (2) influences from composers, (3) nature, (4) his theory of dream, number and water, (5) words and music, (6) East and West, and (7) relationships with other artists including performers. The final chapter is devoted to the piano compositions by Takemitsu, including a comparative and idiomatic analysis that incorporates discussion of the specific creative influences on each work. Aspects of Takemitsu's individuality and the manifestations of his beliefs - both musical and philosophical - are discussed to discover his complex aesthetic heritage. As his own words reveal: "When I decided to be a compser, I did not even know how to notate on scores. In this regard, no one has taught me. These can be learned through reading theory books. But more importantly, things that have established me as a composer are, though those [theory books] do have a little to do with it, things like a book I read, a friend I got to know, or a picture ..."