Michail Peramatzis presents a new interpretation of Aristotle's view of the priority relations between fundamental and derivative parts of reality, following the recent revival of interest in Aristotelian discussions of what priority consists in and how it relates existents. He explores howin Aristotle's view, in contradistinction with (e.g.) Quinean metaphysical views, questions of existence are not considered central. Rather, the crucial questions are: what types of existent are fundamental and what their grounding relation to derivative existents consists in. It is extremelyimportant, therefore, to return to Aristotle's own theses regarding priority and to study them not only with exegetical caution but also with an acutely critical philosophical eye. Aristotle deploys the notion of priority in numerous levels of his thought. In his ontology he operates with the notion of primary substance. His Categories, for instance, confer this honorific title upon particular objects such as Socrates or Bucephalus, while in the Metaphysics it is essences orsubstantial forms, such as being human, which are privileged with priority over certain types of matter or hylomorphic compounds (either particular compound objects such as Socrates or universal compound types such as the species human). Peramatzis' chief aim is to understand priority claims of thissort in Aristotle's metaphysical system by setting out the different concepts of priority and seeing whether and, if so, how Aristotle's preferred prior and posterior items fit with these concepts.