The relation of ontological dependence or grounding, expressed by the terminology of separation and priority in substance, plays a central role in Aristotle’s Categories, Metaphysics, De Anima and elsewhere. The article discusses three current interpretations of this terminology. These are drawn along the lines of, respectively, modal-existential ontological dependence, essential ontological dependence, and grounding or metaphysical explanation. I provide an opinionated introduction to the topic, raising the main interpretative questions, laying out a few of the exegetical and philosophical options that influence one’s reading, and locating questions of Aristotle scholarship within the discussion of ontological dependence and grounding in c...