ABSTRACT This essay investigates and describes the political regime that dominated much of Irish political life in the twentieth century. It was marked by the rise, and eventual fall, of Fianna Fáil as the nation's government party. It charts the creation of the Fianna Fáil regime – the building of a government party to manage a state deliberately cast in its own terms – and then identifies and explores the long decade that saw the slow collapse of both. In the aftermath, the fragmentation of national political competition, and the challenges to the constitutional framework, have left a political regime bereft of the party and constitutional frames that long defined its core political moorings.