Between 1916 and 1923 Ireland experienced a political as well as a military revolution. This book examines how, after the Easter Rising of 1916, radical revolutionaries formed a precarious coalition with (relatively) moderate politicians, offering a sustained analysis of the political organisation of Irish republicanism during a crucial period. The new Sinn FEin party routed its enemies, co-operated uneasily with the underground Irish government which it had helped to create, and achieved most of its objectives before disintegrating in 1922. Its rapid collapse should not distract from its achievements - in particular its role in 'democratising' the Irish revolution. Its successors have dominated the political life of independent Ireland. The book studies in some detail the party's membership and ideology, and also its often tense relationship with the Irish Republican Army. A final chapter examines the fluctuating careers of the later Sinn FEin parties throughout the rest of the twentieth century.