The introduction sets out the theoretical, methodological, and empirical basis for this study. This research explores the evolution of Irish nationalism in Britain through four thematic lenses: the Irish Revolution, British politics, the Irish diaspora, the British Empire. Read collectively, these analytical frameworks can sharpen historical perspectives on the ideological development, communal function, and individual expression of Irish nationalism. To explore the history of the Irish in Britain between 1912 and 1922 is to interrogate a ‘crisis of (national) identity’ in terms of both ‘self’ and ‘other’. Original conceptual frameworks are supported by ‘new’ methodological approaches. Following the linguistic turn of the ‘new’ political history, this study explores representations of Irish nationalism in Britain in the ‘cultural’ spaces between ‘high politics’ and ‘history from below’: political platforms, texts, and languages. This study investigates the Irish Home Rule and republican movements using underutilised archival sources. The T.P. O’Connor papers, Art Ó Briain papers, and Catholic Herald newspaper series collectively establish a robust archival foundation by which to evaluate the significance of Irish nationalism in Britain during the Irish Revolution. The book is divided into five chapters which chronologically, and thematically, examine Irish nationalism in Britain between 1912 and 1922.