The Laigin were a population group of early Ireland who gave their name to the province of Leinster (Irish language Cúige Laighean, "province of the Laigin"; the English word "Leinster" is derived from Irish Laigin plus Old Norse staðr, "place, territory"). According to legend they were descended from the Gaulish warriors who came to Ireland with the returning exile Labraid Loingsech, and are named after the spears (láigne) they carried. Two other population groups, the Gáileóin and the Domnainn, are normally considered as part of the Laigin confederation.
Laigin is a plural noun, indicating an ethnonym rather than a geographic term. The use of the word cuige, earlier cóiced, literally "fifth", to mean "province", implies the existence at some point in prehistory of a pentarchy, whose five members were the Laigin (Leinster), the Ulaid (Ulster), the Connachta (Connacht), Mumu (Munster), and probably Mide (Meath), a central province whose name survives in Counties Meath and Westmeath, although the original Mide was more extensive than those counties.