This book is the first systematic study of Neo-Platonist philosopher Proclus’ theory of the bad. Examining Proclus’ overall system demonstrates that his critique of Plotinus’ attribution of all ill to the material is cogent. Moreover, a comparison between Proclus and Plato shows that the Proclus’ theory of the ethical bad can be plausibly construed as an interpretation of Plato’s theory of action. Finally, examining the similarities between Dionysius Areopagita’s theory of the bad and Proclus’ preceding theory allows one to discern which elements of Dionysius’ view are of his own creation and which are borrowed from his predecessors.