Are there nonexistent things? What is the nature of informative identity statements? Are the notions of essential property and of essence intelligible, and, if so, how are they to be understood? Are individual things material substances or clusters of qualities? Can the account of the unity of a complex entity avoid vicious infinite regresses? These questions have attracted widespread attention among philosophers recently, as evidenced by a proliferation of articles in the leading philosophical journals. In Being Qua Being they receive systematic, unified treatment, grounded in an account of the nature of the application to the world of our conceptual apparatus. A central thesis of the book is that the topic of identity is primary, and that existence and predication, both essential and accidental, are to be understood in terms of identity.