Irish Republican Army (IRA), a revolutionary organization whose objective is to create a united Ireland independent of British rule. The IRA has been illegal since 1936, but was long tolerated by the Irish Republic because of public sentiment for unification. After the Provisionals (a group of extremists within the IRA) began a terrorist campaign against Northern Ireland and Great Britain in the early 1970's, the Irish government moved to suppress the IRA. The IRA shares common goals with Sinn Fein, an Irish political party that functions as its legal political arm.

When Ireland declared its independence from Britain in 1919, existing private revolutionary armies became the Irish Republican Army, which fought the British until Britain permitted southern Ireland to found the Irish Free State in 1921. Although the Irish government accepted separation from Northern Ireland, the IRA opposed it, often with violence. When Eamon de Valera, prime minister of the Irish Free State, outlawed the IRA in 1936, it went underground. It engaged in terrorist acts, 1956–62, and became active again in 1969 when riots occurred between Catholics and Protestants in Northern Ireland. The Provisionals split off from the main group soon afterward.

In 1979 members of the Provisional IRA assassinated Lord Mountbatten, uncle of Prince Philip and the retired head of the British armed forces. Hunger strikes in 1981 by British-held Provisional prisoners, which ended in several deaths, precipitated severe rioting in Northern Ireland.

Terrorist attacks by the Provisional IRA occurred throughout the 1980's and early 1990's. In 1994, leaders of the Provisional IRA agreed to end hostilities in return for Sinn Fein's inclusion in Anglo-Irish negotiations over the future of Northern Ireland. Negotiations broke down and terrorism resumed in 1996. A Good Friday peace accord, which involved a power-sharing arrangement, was signed by the parties in 1998, but suspended in 2002 pending disarmament of the IRA. In 2005 the IRA renounced the use of violence to achieve its ends.