The thesis comprises three major parts. In Part I, existing writing, both published and unpublished, on the history of school libraries, is surveyed, showing that there is available no comprehensive history of school libraries, or even of school libraries in a country or region. In Part II, the development of school libraries is traced from the eighth century library at York to the school library media centres of the present day, with emphasis on British, American, and Australian school libraries. This chronological survey covers medieval English school libraries, the libraries of the grammar schools of sixteenth and seventeenth century Britain, the elementary and Sunday school libraries of the nineteenth century, the libraries of "public", academy, and independent secondary schools in the eighteenth and nineteenth centuries, and the secondary, elementary, and Sunday school libraries of the twentieth century. In Part III, "Concepts of the School Library", the development of school libraries is considered in terms of the reasons for which such libraries have been established and maintained over the centuries. The five types of school library discussed are: the school library established to support the teaching and learning activities of the school; the school library established to provide recreational reading; the library established to serve both the school and the community; the school library established as a scholars' library to serve the needs of a particular group within the school; and the school library established as a memorial. The aim of the thesis has been to show that school library provision is a great deal older than has generally been assumed, and that the reasons for which the school libraries have been established and maintained have changed but little over the centuries.