For Jews and Christians in Antiquity beliefs about demons were integral to their reflections on fundamental theological questions, but what kind of 'being' did they consider demons to be? To what extent were they thought to be embodied? Were demons thought of as physical entities or merely as metaphors for social and psychological realities? What is the relation between demons and the hypostatization of abstract concepts (fear, impurity, etc) and baleful phenomenon such as disease? These are some of the questions that this volume addresses by focussing on the nature and characteristics of demons - what one might call 'demonic ontology'.