The Official Irish Republican Army or Official IRA (OIRA; Irish: Óglaigh na hÉireann) was an Irish republican paramilitary group whose goal was to remove Northern Ireland from the United Kingdom and create a "workers' republic" encompassing all of Ireland. It emerged in December 1969, shortly after the beginning of the Troubles, when the Irish Republican Army (IRA) split into two factions. The other was the Provisional IRA. Each continued to call itself simply "the IRA" and rejected the other's legitimacy. Unlike the "Provisionals", the "Officials" did not think that Ireland could be unified until the Protestant majority of Northern Ireland and Catholic minority of Northern Ireland were at peace with each other. The Officials were Marxist-Leninists and worked to form a united front with other Irish communist groups, named the Irish National Liberation Front (NLF). The Officials were called the NLF by the Provisionals, the "stickies" by nationalists in Belfast (apparently in reference to members who would glue Easter lilies to their uniforms), and were sometimes nicknamed the "Red IRA" by others.It waged a limited campaign against the British Army, mainly involving shooting and bombing attacks on troops in urban working-class neighbourhoods. Most notably, it was involved in the 1970 Falls Curfew and carried out the 1972 Aldershot bombing. In May 1972, it declared a ceasefire and vowed to limit its actions to defence and retaliation. By this time, the Provisional IRA had become the larger and more active faction. Following the ceasefire, the OIRA began to be referred to as "Group B" within the Official movement. It became involved in feuds with the Provisional IRA and the Irish National Liberation Army (INLA), an OIRA splinter group formed in 1974. It has also been involved in organized crime and vigilantism.

The Official IRA was linked to the political party Official Sinn Féin, later renamed Sinn Féin – the Workers Party and then the Workers' Party of Ireland.