This detailed study of Berkeley's metaphysics and epistemology concentrates on the views expressed in the Three Dialogues between Hylas and Philonous (1713). The book is written for advanced undergraduates, graduate students, and academics in philosophy who are not specialists in the early modern period, and it shows that Berkeley is an important and systematic thinker whose work is still of relevance to philosophers today. Discussion of secondary literature is kept to a minimum (there are no footnotes) and the interpretation defended maximizes the strength of Berkeley's arguments and the plausibility of his views. Part 1 is a general overview. In Part 2, Berkeley is shown to be a direct realist about perception of the physical world who denies that the objects of either perception or of scientific theory are material. In Part 3, Berkeley's positive views on substance, causation, action, free will, universals, concepts, identity, and persistence are also considered. While Berkeley's immaterialism is criticized, its weaknesses are shown to lie in the details rather than in the big picture, which is no more implausible or unattractive than the materialist alternatives.