It is now time for a comprehensive treatise to look at the whole field of electrochemistry. The present treatise was conceived in 1974, and the earliest invitations to authors for contributions were made in 1975. The completion of the early volumes has been delayed by various factors. There has been no attempt to make each article emphasize the most recent situation at the expense of an overall statement of the modern view. This treatise is not a collection of articles from Recent Advances in Electrochemistry or Modern Aspects of Electrochemistry. It is an attempt at making a mature statement about the present position in the vast area of what is best looked at as a new interdisciplinary field. Texas A & M University J. O'M. Bockris University of Ottawa B. E. Conway Case Western Reserve University Ernest Yeager & M University Texas A Ralph E. White Preface to Volume 2 This volume brings together some dozen processes well known to the electro­ chemist and treats them according to their various degrees of importance. The production of hydrogen is one of the more important processes, particularly with respect to the prospects of a hydrogen economy. No one would doubt, however, that the most commercially important electrochemical processes at the present time are the production of aluminum and of chlorine. Each of these processes has a separate chapter devoted to it.