This book argues that Western philosophy's traditional understanding of Being as substance is incorrect, and demonstrates that Being is fundamentally Relationality. To make that argument, the book examines the history of Western philosophy's evolving conception of being, and shows how this tradition has been dominated by an Aristotelian understanding of substance and his corresponding understanding of relation. First, the book establishes that the original concept of Being in ancient Western philosophy was relational, and traces this relational understanding of Being through the Neoplatonists. Then, it follows the substantial understanding of Being through Aristotle and the Scholastics to reach its crisis in Descartes. Finally, the book demonstrates that Heidegger represents a recovery of the original, relational understanding of Being.