This book examines the rise and fall of the aristocratic Lacy family in England, Ireland, Wales and Normandy. This involves a unique analysis of medieval lordship in action, as well as a re-imagining of the role of English kingship in the western British Isles and a rewriting of seventy-five years of Anglo-Irish history. By viewing the political landscape of Britain and Ireland from the perspective of one aristocratic family, this book produces one of the first truly transnational studies of individual medieval aristocrats. This results in an in-depth investigation of aristocratic and English royal power over five reigns, including during the tumultuous period of King John and Magna Carta. By investigating how the Lacys sought to rule their lands in four distinct realms, this book also makes a major contribution to current debates on lordship and the foundations of medieval European society.