The object of this book is to provide an introduction to electro chemistry in its present state of development. An attempt has been made to explain the fundamentals of the subject as it stands today, de voting little or no space to the consideration of theories and arguments that have been discarded or greatly modified. In this way it is hoped that the reader will acquire the modern point of view in electrochemistry without being burdened by much that is obsolete. In the opinion of the writer, there have been four developments in the past two decades that have had an important influence on electrochemistry. They are the ac tivity concept, the interionic attraction theory, the proton-transfer theory of acids and bases, and the consideration of electrode reactions as rate processes. These ideas have been incorporated into the structure of the book, with consequent simplification and clarification in the treatment of many aspects of electrochemistry. This book differs from the au thors earlier work, The Electrochem istry of Solutions in being less comprehensive and in giving less detail. While the latter is primarily a work of reference, the present book is more suited to the needs of students of physical chemistry, and to those of chemists, physicists and physiologists whose work brings them in con tact with a variety of electrochemical problems. As the title implies, the book should also serve as an introductory text for those who in tend to specialize in either the theoretical or practical applications of electrochemistry. In spite of some lack of detail, the main aspects of the subject have been covered, it is hoped impartially and adequately. There has been some tendency in recent electrochemical texts to pay scant attention to the phenomena at active electrodes, such as ovcrvoltage, passivity, cor rosion, deposition of metals, and so on. These topics, vihich are of importance in applied electrochemistry, are treated here at Mich length as seems reasonable. In addition, in view of tho growing interest in electrophoresis, and its general acceptance as a branch of electrochem istry, a chapter on clectrokinetic phenomena has boon included. No claim is made to anything approaching completeness in the matter of references to the scientific literature. Such reformers as arc given arc generally to the more recent publications, to review articles, and to papers that may, for one reason or another, have some special interest. References are also frequently included to indicate the sources from which data have been obtained for many of the diagrams and tables. Since no effort was made to be exhaustive in this connection, it was felt that an author index would be misleading...