Wittgenstein is the most influential twentieth century philosopher in the English-speaking world. In the Philosophical Investigations, his most important work, he introduces the famous 'private language argument' which changed the whole philosophical view of language. Wittgenstein and the Philosophical Investigations introduces and assesses Wittgenstein's life, and its connection with his thought; the text of the Philosophical Investigations; and the importance of Wittgenstein's work to contemporary philosophy.