In this book, James Filler traces the history of Being, understood as substance, from Parmenides through the Scholastics and ending with Descartes, in whom this understanding reaches a crisis. He further shows how this understanding inherently leads to serious ontological problems which are unresolvable within a substance ontological approach. It is this substance understanding which has dominated, but this view--with its emphasis on distinctness, independence, and separateness--will create insurmountable problems which ultimately lead to a crisis of thought after Descartes. The book examines this substance understanding, how it has historically shaped the understanding of Being, and how this understanding ultimately becomes ontologically and epistemologically destructive. James Filler teaches philosophy at Wheeling University (USA). He is author of Heidegger, Neoplatonism, and the History of Being (Palgrave, 2023), and was winner of the 2021 Review of Metaphysics Dissertation Essay Contest.