The High King of Ireland (Irish language: Árd Ri) was the nominal head of the gaelic policy that existed before English rule in Ireland. An all-island Ireland state did not exist prior to the English creation of the Lordship of Ireland. Gaelic Ireland consisted of numerous small kingdoms. The High King was the premier member of the gaelic governing class. His role was not however comparable with a 'king of Ireland'. Depending on the personality and strengths of the holder of the office, however, it could exercise an authority beyond its normal role.

The High King of Ireland lived in Tara in County Meath, approximately 25 miles to the North West of the modern day capital, Dublin. Nothing physical remains of the ancient site except outlines of mounds on which wooden buildings stood.

The most famous and powerful High King of Ireland was Brian Boru, the King of Munster.

The last High King of Ireland was Rory O'Connor. His descendant, the O'Connor Don, is the claimant to the Irish throne.

See also List of High Kings of Ireland