First in-depth investigation of the genealogies of medieval Wales, bringing out their full significance. Genealogy was a central element of life in medieval Wales. It was the force that held society together and the framework for all political action. For these reasons, genealogical writing in medieval Wales, as elsewhere in Europe, became a fundamental tool for representing and manipulating perceptions of the socio-political order across historical and literary time. From its beginnings within an early medieval Insular genre of genealogical writing, Welsh genealogy developed across the Middle Ages as a unique and pervasive phenomenon. This book provides the first integrated study of and comprehensive introduction to genealogy in medieval Wales, setting it in the context of genealogical writing from Ireland, England and beyond and tracing its evolution from the eighth to the sixteenth century. The three most important collections of secular genealogies are carefully analysed and their composition is considered in relation to medieval Welsh politics. Particular attention is devoted to the pedigrees of the kings and princes of Gwynedd, which were subject to many intricate alterations over time. The book also includes fresh critical editions of the most significant extant collections of secular genealogy.