Irish Republicans found themselves at a crisis moment in 1949. Legislation enacted by each state on the island affirmed the political reality of Ireland’s partition. The Southern state declared an Irish Republic while the Northern state affirmed Northern Ireland’s continuing integration with the United Kingdom. The partition of island between these two governments was reinforced by the Irish border in the 1950s as it had been for the previous three decades. The Irish Republican Army remained committed to ending the separation through force while the Northern Ireland security apparatus steadfastly safeguarded the realm against any foreign incursion or domestic insurrection. Irish Republicanism reorganized and the IRA launched a disastrously planned and under-resourced Border Campaign between 1956 and 1962. The IRA was fully repelled by the Northern security forces: the Royal Ulster Constabulary supported by the Special Constabulary with security assistance from the governments in Belfast, London and, eventually, Dublin. The militant aspect was accompanied by political measures that reaped electoral gains and signs of public support peaking in the mid-1950s before a clear repudiation of the movement by the end of the decade. By the start of the 1960s, the IRA had been defeated and Irish Republicanism was reeling, unsure of its future political vitality and social relevance. Northern Ireland and the Irish border was more secure than at any point in its previous 40 years of existing, ruled by a strong, confident British Unionist hegemony. For Irish Republicans living on the frontier of the Northern Ireland state, new modes of political thinking and confrontational actions with the state had been attempted and ultimately abandoned. This project examines the main dynamics at play along the Irish border between 1949 and 1961. Focus will be on the Sinn Féin, the IRA and Liam Kelly’s Republican splinter group Saor Uladh, the RUC, B-Specials and militant-political Unionism, and the role of governments in Belfast, Dublin and London during the costly decade of the 1950s.