The MacDonnells of Antrim (Gaelic: Mac Domhnaill), also known as the MacDonnells of the Glens, are a branch in Ireland of the Scottish-based Clan Donald. Initially part of Clan MacDonald of Dunnyveg (Clan Donald South), the MacDonnells of Antrim became their own branch in 1558 when Somhairle Buidhe MacDonnell obtained the lordship of the territory in Ireland from James MacDonald, 6th chief of the Clan MacDonald of Dunnyveg.
The MacDonnells of Antrim were a sept of the Clan Donald of the royal Clann Somhairle, that the English crown had attempted to cultivate since the early 14th century in its efforts to influence the course of politics in Scotland. The MacDonnells established a growing presence in Ireland throughout the 15th and 16th centuries, and played a crucial role in the politics of 17th century Ireland. The MacDonnell's achieved much success in Ireland largely to cultural and familial connections to the Gaelic nobility of Ireland.