The most influential philosopher in the analytic tradition of his time, Willard Van Orman Quine (1908-2000) changed the way we think about language and its relation to the world. His rejection of the analytic/synthetic distinction, his scepticism about modal logic and essentialism, his celebrated theme of the indeterminacy of translation, and his advocacy of naturalism have challenged key assumptions of the prevailing orthodoxy and helped shape the development of much of recent philosophy. This introduction to Quine's philosophical ideas provides philosophers, students, and generalists with an authoritative analysis of Quine's lasting contributions to philosophy. The major themes covered include the adaptation of the language of modern logic to formulate a criterion of ontological commitment; Quine's own ontological commitments; Duhemian-Holistic empiricism and the attendant rejection of a priori knowledge; the nature and grounds of logical truth; Quine's criticisms of such notions as meaning, synonymy, analyticity, and necessity; the conjecture of the indeterminacy of translation; modal logic; propositional attitudes; and Quine's work on naturalized epistemology. Quine's ideas throughout are contrasted with more traditional views, as well as with contemporaries such as Frege, Russell, Carnap, Davidson, Field, Kripke, and Chomsky, enabling the reader to grasp a clear sense of the place of Quine's views in twentieth-century philosophy and the important criticisms of them.