The Irish Socialist Republican Party (ISRP) was a party of seminal importance in the history of radical politics in modern Ireland. The party was the forerunner and ideological springhead for a political tradition that has had a significant impact on radical Irish politics ever since. The ISRP was the first experiment with that powerful, dynamic, yet sometimes very confused cocktail of traditional republican politics and socialist principles.The party produced the first regular socialist paper in Ireland The Workers’ Republic , ran candidates in local elections, represented Ireland at the Second International, agitated over issues such as the Boer War and the 1798 commemorations. Politically, the ISRP was before its time, putting the call for an independent Republic at the centre of its propaganda before Sinn Fein or others had done so. This is the first full-length study of this important organisation. Using the primary sources available this study delves into the internal politics and personalities that brought life to the organisation. The political significance of the organisation led by James Connolly is also viewed in both the international and national sphere. The legacy of the ISRP was to have an impact on the left wing and republican movements in Ireland for many decades following its demise in 1904.