This study deals with the nature, development and consequences of nationalist movements in Wales. In 1973, a Royal Commission on the Constitution recommended the establishment of legislative assemblies in Cardiff and Edinburgh. The study begins with an analysis of the maintenance of a sense of national distinctiveness in Wales and Scotland, despite centuries of political incorporation into the United Kingdom. The thesis shows how the different stages of development of Welsh and Scottish societies at the time of unification with England was crucial in terms of the maintenance of national institutions. Whereas Scotland maintained a series of significant national institutions, in Wales the Welsh language became a major prop of national identity. Part of this work analyses the fate of the Welsh language since unification and its role in religion, education and the formation of political identity. The enduring link between language and nationality is examined, as is the role of the language in the development of Welsh nationalist ideology in the twentieth century. The thesis also examines-the changing social, economic and occupational structure of Wales since 1945 in an attempt to explain the growth in support of Plaid Cymru in the nineteen sixties. The proposals to create legislative assemblies were the subject of a referendum in 1979, and the debate over the devolution proposals is also analysed. The thesis concludes with a review of the relevant literature, a discussion of the relative neglect by sociologists of nationalism and nationalist movements and an assessment of the future prospects for the Welsh nationalist movement.