Ludwig Wittgenstein's Tractatus Logico-Philosophicus is among the most ambitious and influential philosophical works of the early twentieth century, and in recent years it has again occupied a central position in discussions of Wittgenstein's philosophy. Written in an austere and meticulous style, the Tractatus addresses questions in the philosophy of language, logic, and metaphysics, and, according to its author, provides a solution to all the problems of philosophy. This student-oriented edition contains the original English translation by C.K. Ogden and Frank P. Ramsey, annotated and revised by the editor to improve its accuracy and clarity. Appendices include important material by Gottlob Frege, Bertrand Russell, and from Wittgenstein's other writings.