The thesis traces the development of the rural library service in Ireland between 1902 and 1935, with particular reference to the part played by Andrew Carnegie and the Carnegie United Kingdom Trust, which he established in 1913, in that development. The first chapters explore the nineteenth century background. The variety of library facilities that existed in Britain and Ireland - ranging from Mechanics' Institutes to parish libraries, are described. In Ireland the belief that books could rehabilitate the countryside and revive the National spirit gained rural libraries the support of agricultural co-operators and cultural nationalists. The Public Library Act of 1902 enabled Rural District Councils to raise a library rate. Between 1902 and 1914 a number of organisations promoted rural libraries, while others expressed scepticism. These opposing groups are described, and the difficulties of providing a rural library service is shown by a study of one such service in Rathkeale rural district, County Limerick. In 1915 the Carnegie United Kingdom Trust appointed Lennox Robinson as organiser of libraries in County Limerick. His work described, and the extension of his responsibilities to become the Trust's Irish representative is traced. In 1917 the trustees established an Irish advisory committee, and from 1921 financed experimental county library schemes. The first two schemes, in Counties Donegal and Antrim, are described in detail. Acts of parliament passed in 1924 and 1925 made County Councils the library authorities in Northern Ireland and the Irish Free State. This encouraged the Carnegie trustees to change their library policy, a decision precipitated by a public controversy caused by a short story written by Robinson. This incident is described, together with its consequences. The final chapter follows the fortunes of the county library service from 1925 to 1935 and describes how libraries were affected by the political and moral climate of the time. The thesis concludes with the Carnegie trustees' decision to cease funding county library services from 1935.