This book has been planned and written by Dr. Hine with his knowledge and experience in electrochemical science and engineering for over thirty years since he joined with me at Kyoto University in 1948. This book is unique and is useful for engineers as well as scientists who are going to work in any interdisciplinary field connected with elec­ trochemistry. Science is sure to clarify the truth of nature as well as bring prosperity and an improvement to the welfare of human beings. The origin of the word "science" is the same as of "conscience," which means the truth of our heart. When we consider a scientific and technological subject, first we classify it into the components and/or factors involved, and then we clarify them individually. Second, we combine them to grasp the whole meaning and feature of the subject under discussion. Computers may help us greatly, but how to establish the software that will be most desirable for our purposes is of great importance. We need to make these efforts ourselves, and not decorate with borrowed plumes. With this concept in mind, this book is attractive because the author describes the basic science in electrochemistry and practice, and discusses the electrochemical engineering applications as a combination of science and technology.