This book studies early Irish and Welsh kinship. Kinship is a central element in all human societies. It was of particular significance in early medieval Ireland and Wales where governmental institutions were, in general, weak. This book examines the forms of kinship found in Ireland and Wales at the earliest periods for which documentation is sufficient (the 7th century for Ireland and the 12th–13th centuries for Wales). The book's analysis of kinship vocabulary and careful consideration of the available evidence enables the book to take the discussion back to earlier periods.