Irish clans are traditional kinship groups sharing a common surname and heritage and existing in a lineage-based society, originating prior to the 17th century.[1] A clan (or fine in Irish, plural finte) included the chief and his patrilineal relatives;[2] however, Irish clans also included unrelated clients of the chief.[3] These unrelated clients and their agnatic descendants were ineligible to be elected chief, but nonetheless assumed the name of the leading lineage as a show of allegiance.[4]
Many genealogies have been compiled over the centuries purporting to trace the ancestry of these clans. Among them are genealogies in Rawlinson B 502, the Book of Ballymote, the Book of Lecan, the Leabhar Mór na nGenealach compiled by Dubhaltach MacFhirbisigh, and the Ó Cléirigh Book of Genealogies. In all of these cases, the genealogies listed state the agnatic descent of the chiefs and chieftains, and not necessarily every member of the clan.