The objective of the present volume is to develop the theory and practice of nonmetal electrochemistry from first principles, emphasizing energy level models, in particular the fluctuating energy level model of Marcus and Gerischer. A single volume emphasizing these models. and the in­ terpretation of experiments based on these models, has not been available. Yet this area of electrochemical technology, where the use of such models is required, has developed a great deal of interest. This is not only because of the interest in photoelectrochemical solar cells, but also because of the importance of the concepts in corrosion, sensors, coated metal electrodes, and, indeed, to the general theory of electrode reactions. This book is an attempt to fill the void-to develop in a single volume the basic description of electrode reactions on nonmetallic electrodes and oxide-covered metal electrodes. The development of the fluctuating energy level model to describe electrode reactions on nonmetals (as described in Chapters I through 3) has permitted a significant forward step in the understanding of such re­ actions. The power of the model is illustrated by the simple methods available to determine the energy levels of interest-the conduction and valence bands of the nonmetals (Chapter 5), and their relation to the energy levels of oxidizing or reducing agents in solution. In Chapter 6, we illustrate the ability of the simple models. based on these parameters, to describe successfully electrode reactions at an inert electrode.