In the first part of the book, Dale Jacquette explores questions of pure philosophical ontology: what is meant by the concept of being, why does something exist rather than nothing, and why there is only one logically contingent actual world. The author argues that logic provides the only possible answers to these fundamental problems of pure ontology. In the second part of the book Jacquette examines issues of applied scientific ontology and provides a critical survey of some of the most influential traditional ontologies, such as the distinction between appearance and reality and the categories of substance and transcendence. The ontology of physical entities - space, time, matter, and causation - are examined as well as the ontology of abstract entities - sets, numbers, properties, relations, and propositions. The special problems posed by the subjectivity of mind and of God are also explored. The book concludes with a chapter on the ontology of culture, language, and art.