The purpose of this book is to convey the fundamentals of electrochemistry to the reader in the simplest and most understandable form, even for non-specialists. It therefore requires only a minimum of prior knowledge in chemistry and physical chemistry. For this reason, it serves as a textbook but is also a practical guide, as I have collected and compiled many numerical data in tabular form that are scattered throughout the literature and often not easily accessible. It is impossible to present the entire theory and all applications of electrochemistry in one volume without making it overly bulky. This book primarily develops that part of the theory that is too specialized to find a place in a work on general physical chemistry and secondly examines how the general concepts, already known from the study of physical chemistry and further developed in this book in the specific electrochemical direction, can be applied to electrochemical processes. In my presentation, I have always aimed to highlight not only the results that are part of our established knowledge but also the difficulties and uncertainties that still exist in both theoretical and experimental fields.