In this non-technical introduction the author explains the nature of Wittengenstein's thought, and its impact on contemporary philosophy. Grayling distinguishes between an earlier period up until the completion of the work Tractatus logico-philosophicus, published in 1921, and Wittgenstein's return to philosophy some years later when he worked out a new approach to the questions of thought, language, mind and knowledge. The book compares and contrasts the two periods of Wittgenstein's thought and the influence of his teachings on contemporaries.