It has been fashionable to describe electrochemistry as a discipline at the interface between the branches of chemistry and many other sciences. A perusal of the table of contents will affirm that view. Electrochemistry finds applications in all branches of chemistry as well as in biology, biochemistry, and engineering; electrochemistry gives us batteries and fuel cells, electroplating and electrosynthesis, and a host of industrial and technological applications which are barely touched on in this book. However, I will maintain that electrochemistry is really a branch of physical chemistry. Electrochemistry grew out of the same tradition which gave physics the study of electricity and magnetism. The reputed founders of physical chemistry-Arrhenius, Ostwald, and van't Hoff-made many of their contributions in areas which would now be regarded as electrochemistry. With the post-World War II capture of physical chemistry by chemical physicists, electrochemists have tended to retreat into analytical chemistry, thus defining themselves out of a great tradition. G. N. Lewis defined physical chemistry as "the study of that which is interesting." I hope that the readers of this book will find that electrochemistry qualifies.