The Ulaid (Old Irish, pronounced [ˈʊləðʲ]) or Ulaidh (modern Irish, pronounced [ˈʊləɣʲ]) were a people of early Ireland who gave their name to the modern province of Ulster (modern Irish: Cúige Uladh, pronounced [/ˈkuːiɡʲə ˈʊləɣ/], meaning "fifth-part of the Ulaidh"). The English word Ulster derives from Irish Ulaidh and Old Norse staðr (meaning "place, territory").

In medieval texts they are also referred to as the Clanna Rudraige (modern spelling: Clanna Rudhraighe, anglicization: Clanna Rury) meaning "descendants of Rudraige" – whence the modern Irish term Rúraíocht (the Ulster Cycle of Irish mythology).

Ulaid is a plural noun, indicating an ethnonym rather than a geographic term. The Ulaid are probably mentioned in Ptolemy's 2nd century Geographia, as the Ούολουντοι (Uolunti), probably a corruption of Ούλουτοι (Uluti). The name is probably derived from ul, "beard". The general scholarly consensus since as early as the time of Eoin MacNeill has been that the Ulaid were apparently kin to the so-called Érainn, or at least to their royal families, sometimes called the Clanna Dedad, and perhaps not their nebulous subject populations.T. F. O'Rahilly notably believed the Ulaid were an actual branch of the Érainn. In any case, certainly related to the Ulaid are the less widely known Dáirine, also another name for the Érainn royalty, and both were related to or derived from the Darini of Ptolemy.