This is a new edition of the first volume of G.P. Baker and P.M.S. Hacker's definitive reference work on "Wittgenstein's Philosophical Investigations". This title takes into account much material that was unavailable when the first edition was written. Following Baker's death in 2002, P.M.S. Hacker has thoroughly revised the first volume, rewriting many essays and sections of exegesis completely. Part One - the Essays - now includes two completely new essays: "Meaning and Use" and "The Recantation of a Metaphysician". Part Two - Exegesis 1-184 - has been thoroughly revised in the light of the electronic publication of "Wittgenstein's Nachlass", and includes many new interpretations of the remarks, a history of the composition of the book, and an overview of its structure. The revisions will ensure that this remains the definitive reference work on Wittgenstein's masterpiece for the foreseeable future.