This volume collects the most important articles on the metaphysics of modality by noted philosopher Alvin Plantinga. The book chronicles Plantinga's thought from the late 1960's to the present. Plantinga here is concerned with fundamental issues in metaphysics: what is the nature of abstract objects like possible worlds, properties, propositions, and such phenomena? Are there possible but non-actual objects? Can objects that do not exist exemplify properties? In this thorough and searching book, Plantinga addresses these and many other questions that continue to preoccupy philosophers in the field. This volume contains some of the best work in metaphysics from the past 30 years, and will remain a source of critical contention and keen interest among philosophers of metaphysics and philosophical logic for years to come.