Published to widespread acclaim between 1980 and 1996, the monumental four- volume Analytical Commentary on the Philosophical Investigations has become the definitive reference work on Wittgenstein's masterpiece. This revised edition of Volume I, Wittgenstein: Understanding and Meaning, which itself comprises two parts ('Essays' and 'Exegesis §§1-184'), takes into account much material that was unavailable when the first edition was written. Following G.P. Baker's death in 2002, P.M.S. Hacker has thoroughly revised both parts, rewriting many sections completely and often proposing fresh interpretations. Part I: Essays now includes two new essays: 'Meaning and Use' and 'The Recantation of a Metaphysician', while Part II: Exegesis §§1-184 has been exhaustively reworked in the light of the electronic publication of Wittgenstein's Nachlass. These revisions will ensure that this remains the essential reference work on the Philosophical Investigations for the foreseeable future.