The Irish Republican Army (IRA) (Irish: Óglaigh na hÉireann), sometimes known later as the Old IRA, was a military organisation descended from the Irish Volunteers which was recognised in 1919 by Dáil Éireann as the legitimate army (from the perspective of Irish republicans) of the unilaterally declared Irish Republic, the Irish state proclaimed in the Easter Rising in 1916 and reaffirmed by the Dáil in January 1919. In Irish, it was referred to as Óglaigh na hÉireann.
Though a series of organisations later claimed to be a continuation of the IRA from the 1920s to today, many Irish people disagree with these claims. After the signature of the Anglo-Irish Treaty in 1921, members of the IRA who supported the Treaty formed the nucleus of the National Army founded by IRA leader Michael Collins in 1922. While the anti-Treaty IRA continued to exist after its defeat in the Irish Civil War, by the late 1930s it had lost most of the legitimacy with which most supporters of the Republican side initially regarded it. A small minority of Irish people accepts later claimants to the name as the political heirs of the original Irish Republican Army, though none had their claims accepted by Dáil Éireann.