These papers are of seminal importance to the history of the Labour movement in Ireland, and in particular, the contribution of James Connolly during the period 1898-1916. Labour leader William O'Brien collected a vast amount of material relating, not just to his own extensive involvement in the movement spanning five decades, but also the correspondence and papers of his comrades and associates. There is extensive material in this collection relating to the activities of the left in Dublin from 1898 onwards, including papers pertaining to the Irish Socialist Republican Party of Ireland, founded by James Connolly in 1898, and the Irish Citizen Army, founded by Jack White and James Larkin in 1913. O'Brien collected considerable material relating to the 1913 Lockout and the 1916 Rising, the two most seminal events of his political life, including a vast collection of primary documents consisting of letters, organisational material and propaganda. Papers pertaining to the publication of the Worker's Republic newspaper, edited by James Connolly, and extensive correspondence pertaining to Connolly's endeavours in the United States from 1903-1910, personal letters between Connolly and his wife, and letters between Connolly and his American comrades, are of particular value to researchers. There are also considerable papers covering O'Brien's own involvement in the Labour movement following the Easter Rising, through the turbulence of the War of Independence and the Civil War that followed.