This major study brings Plotinus, the most important philosopher in the centuries between Aristotle and Augustine, into current philosophical discussions. Once neglected among contemporary philosophers, Plotinus' work is attracting greater interest within the context of later Greek philosophy. Lloyd P. Gerson offers a detailed account of Plotinus' arguments in the major philosophical areas of metaphysics, epistemology, psychology and ethics. He examines the work of Plotinus both in its historical context and in its sustained systematic rigor. Focusing on Plotinus' defence of Platonism against Aristotle and on the development of Neoplatonism, Gerson constructs a powerful and systematic account of reality that is surprisingly relevant to modern debates.