The Warrenpoint ambush, also known as the Narrow Water ambush, the Warrenpoint massacre or the Narrow Water massacre, was a guerrilla attack by the Provisional Irish Republican Army (IRA) on 27 August 1979. The IRA's South Armagh Brigade ambushed a British Army convoy with two large roadside bombs at Narrow Water Castle outside Warrenpoint, Northern Ireland. The first bomb was aimed at the convoy itself, and the second targeted the incoming reinforcements and the incident command point (ICP) set up to deal with the incident. IRA volunteers hidden in nearby woodland also allegedly fired on the troops, who returned fire. The castle is on the banks of the Newry River, which marks the border between Northern Ireland and the Republic of Ireland.

Eighteen British soldiers were killed and over twenty were seriously injured, making it the deadliest attack on the British Army during the Troubles. An English civilian was also killed and an Irish civilian wounded, both by British soldiers firing across the border after the first blast. The attack happened on the same day that the IRA assassinated Lord Louis Mountbatten, a member of the British royal family.

The Irish Republican Army (IRA; Irish: Óglaigh na hÉireann), also known as the Provisional Irish Republican Army, and informally as the Provos, was an Irish republican paramilitary organisation that sought to end British rule in Northern Ireland, facilitate Irish reunification and bring about an independent, socialist republic encompassing all of Ireland. It was the most active republican paramilitary group during the Troubles. It saw itself as the army of the all-island Irish Republic and as the sole legitimate successor to the original IRA from the Irish War of Independence. It was designated a terrorist organisation in the United Kingdom and an illegal organisation in the Republic of Ireland, both of whose authority it rejected.

The Provisional IRA emerged in December 1969, due to a split within the previous incarnation of the IRA and the broader Irish republican movement. It was initially the minority faction in the split compared to the Official IRA, but became the dominant faction by 1972. The Troubles had begun shortly before when a largely Catholic, nonviolent civil rights campaign was met with violence from both Ulster loyalists and the Royal Ulster Constabulary (RUC), culminating in the August 1969 riots and deployment of British soldiers. The IRA initially focused on defence of Catholic areas, but it began an offensive campaign in 1970 that was aided by weapons supplied by Irish American sympathisers and Libyan leader Muammar Gaddafi. It used guerrilla tactics against the British Army and RUC in both rural and urban areas, and carried out a bombing campaign in Northern Ireland and England against military, political, and economic targets, and British military targets in Europe.

The Provisional IRA declared a final ceasefire in July 1997, after which its political wing Sinn Féin was admitted into multi-party peace talks on the future of Northern Ireland. These resulted in the 1998 Good Friday Agreement, and in 2005 the IRA formally ended its armed campaign and decommissioned its weapons under the supervision of the Independent International Commission on Decommissioning. Several splinter groups have been formed as a result of splits within the IRA, including the Continuity IRA and the Real IRA, both of which are still active in the dissident Irish republican campaign. The IRA's armed campaign, primarily in Northern Ireland but also in England and mainland Europe, killed over 1,700 people, including roughly 1,000 members of the British security forces, and 500–644 civilians. In addition 275–300 members of the IRA were killed during the conflict.