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 Texas A & M University Ralph E. White Preface to Volume 3 Of events which have affected progress in the field of electrochemistry, the decision of NASA to use electrochemical auxiliary power in space vehicles was one of the more important. Another important decision was Ford's announcement of their sodium-sulfur cell for vehicular use in 1969.