The text Modern Electrochemistry (authored by J. O'M. Bockris and A. K. N. Reddy and published by Plenum Press in 1970) was written between 1967 and 1969. The concept for it arose in 1962 in the Energy Conversion Center at the University of Pennsylvania, and it was intended to act as a base for interdisciplinary students and mature scientists~hemists, physicists, biologists, metallurgists, and engineers-who wanted to know about electrochemical energy conversion and storage. In writing the book, the stress, therefore, was placed above all on lucidity in teaching physical electrochemistry from the beginning. Although this fundamentally undergraduate text continues to find purchasers 20 years after its birth, it has long been clear that a modernized edition should be written, and the plans to do so were the origin of the present book. However, if a new Bockris and Reddy was to be prepared and include the advances of the last 20 years, with the same degree of lucidity as characterized the first one, the depth of the development would have to be well short of that needed by professional electrochemists.