The national flag of Ireland (Irish: bratach na hÉireann), frequently referred to in Ireland as 'the tricolour' (an trídhathach) and elsewhere as the Irish tricolour is a vertical tricolour of green (at the hoist), white and orange. The proportions of the flag are 1:2 (that is to say, flown horizontally, the flag is half as high as it is wide).

Presented as a gift in 1848 to Thomas Francis Meagher from a small group of French women sympathetic to the Irish cause, it was intended to symbolise the inclusion and hoped-for union between Roman Catholics (symbolised by the green colour) and Protestants (symbolised by the orange colour). The significance of the colours outlined by Meagher was, "The white in the centre signifies a lasting truce between Orange and Green and I trust that beneath its folds the hands of Irish Protestants and Irish Catholics may be clasped in generous and heroic brotherhood".

It was not until the Easter Rising of 1916, when it was raised above Dublin's General Post Office by Gearóid O'Sullivan, that the tricolour came to be regarded as the national flag. The flag was adopted by the Irish Republic during the Irish War of Independence (1919–1921). The flag's use was continued by the Irish Free State (1922–1937) and it was later given constitutional status under the 1937 Constitution of Ireland. The tricolour is used by nationalists on both sides of the border as the national flag of the whole island of Ireland since 1916. Thus it is flown by many nationalists in Northern Ireland as well as by the Gaelic Athletic Association.