The metal-insulator transition due to electron-electron interactions is one of the most celebrated but least understood problems in condensed matter physics. Here this subject is comprehensively reviewed for the first time since Sir Nevill Mott's monograph of 1990. A pedagogical introduction to the basic concepts for the Mott transition, the Hubbard model, and various analytical approaches to correlated electron systems is presented. A new classification scheme for Mott insulators as Mott-Hubbard and Mott-Heisenberg insulators is proposed. Traditional methods are critically examined for their potential to describe the Mott transition. This book will make an excellent reference for scientists researching in the field of electron transport in condensed matter.