A key argument of this book is that it is impossible to separate the growth of any insular origin narrative from that of the larger corpus of historical writing which contained them. Chapter One presents the evidence for the textual connections between these works, while the chapters to follow analyse the implications of these connections. This chapter outlines the sources and later reuses of each major work under consideration. Specialists on individual texts and manuscripts will already be aware of many of these connections, yet broader scholarship on the early medieval period still treats so-called ‘Irish’, ‘Welsh’, ‘Anglo-Saxon’ and ‘Scottish’ literary and historical traditions as disparate. This chapter thus provides the ‘hard evidence’ for the extent to which the corpus of texts containing origin narratives influenced one another during the early medieval period. Early medieval authors were interested not solely in writing the story of their own people, but rather, in collecting the histories of the peoples of Britain and Ireland together. Chapter One overturns the common perception that the authors of these texts were working in proto-national isolation, instead revealing the textual connections that shaped the intellectual landscape of the early medieval insular region.