Unavailable for 30 years, this volume presents the original German/English edition of Wittgenstein's Philosophical Investigations - one of the most influential philosophical works of the 20th century. The last product of intensive work by Wittgenstein during the period 1929-49, the book explores the concepts: of meaning; of understanding; of propositions; of logic; and of states of consciousness. The fundamental ideas of the Tractatus are both expounded and criticized. It should be of particular interest to all students of philosophy.