Operation Banner was the operational name for the British Armed Forces' operation in Northern Ireland from 1969 to 2007, as part of the Troubles. It was the longest continuous deployment in British military history. The British Army was initially deployed, at the request of the unionist government of Northern Ireland, in response to the August 1969 riots. Its role was to support the Royal Ulster Constabulary (RUC) and to assert the authority of the British government in Northern Ireland. This involved counter-insurgency and supporting the police in carrying out internal security duties such as guarding key points, mounting checkpoints and patrols, carrying out raids and searches, riot control and bomb disposal. More than 300,000 soldiers served in Operation Banner. At the peak of the operation in the 1970s, about 21,000 British troops were deployed, most of them from Great Britain. As part of the operation, a new locally-recruited regiment was also formed: the Ulster Defence Regiment (UDR).

The Troubles were an ethno-nationalist conflict in Northern Ireland that lasted for about 30 years from the late 1960s to 1998. Also known internationally as the Northern Ireland conflict, it is sometimes described as an "irregular war" or "low-level war". The conflict began in the late 1960s and is usually deemed to have ended with the Good Friday Agreement of 1998. Although the Troubles mostly took place in Northern Ireland, at times violence spilled over into parts of the Republic of Ireland, England, and mainland Europe.