This thesis examines the significance of Catholicism as a political force in Scotland in the years between the restoration of the ecclesiastical hierarchy in 1878 and the Spanish Civil War, exploring the ways in which the Roman Catholic Church sought to assert its presence in Scottish politics and society. Through an examination of the power of the Scottish Church, its affiliated lay organisations and the political attitudes of the laity, this study redresses a historiographical imbalance which has focussed traditionally on the Church's denominational interests in education. The thesis thus provides a reassessment of the political articulation of Catholicism in modern Scotland, of the degree of ideological coherence amongst Catholics, and of the sources of internal division within the community. The issues covered include expatriate Irish nationalism, the growth and consolidation of the political labour movement, the emergence in the early-to-mid 1920s of the Catholic Action movement as well as the relationship between the Catholic Church and the other major Christian denominations in Scotland. Special attention is paid to the formation of the Catholic-Labour electoral alliance, highlighting its overall importance in providing a new impetus to Catholic political engagement. This thematic approach not only permits concentration on different aspects of Catholic interactions with the wider society, but also enhances understanding of the variety of Catholic responses to contemporary political and social developments.