Modal interpretations provide a general framework within which quantum mechanics can be considered as a theory that describes reality in terms of physical systems possessing definite properties. Modal interpretations are relatively new attempts to present quantum mechanics as a theory which, like other physical theories, describes an observer-independent reality. In this book, Pieter Vermaas details the results of this work. He provides both an accessible survey and a systematic reference work about how to understand quantum mechanics using a modal interpretation. The book will be of great value to undergraduates, graduate students and researchers in philosophy of science and physics departments with an interest in learning about modal interpretations of quantum mechanics.