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]
Before the Anglo-Norman invasion of Ireland which took place during the late 12th century, the Irish people were Celts who lived in kinship groups as found recorded in historic manuscripts such as the Irish annals, the Leabhar na nGenealach (the Great Book of Irish Genealogies), the Book of Ballymote, the Great Book of Lecan and Ó Cléirigh Book of Genealogies (the O Clery Book of Genealogies).