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