This series of short texts provides accessible accounts of a range of essential topics in chemistry. Written with the needs of the student in mind, the Oxford Chemistry Primers offer just the right level of detail for undergraduate study, and will be invaluable as a source of material commonly presented in lecture courses yet not adequately covered in existing texts. All the basic principles and facts in a particular area are presented in a clear and straightforward style, to produce concise yet comprehensive accounts of topics covered in both core and specialist courses. This Primer seeks to provide an introduction to the science of equilibrium electrochemistry; specifically, it addresses the topic of electrode potentials and their applications. It builds on a knowledge of elementary thermodynamics giving the reader an appreciation of the origin of electrode potentials and shows how these are used to deduce a wealth of chemically important information and data such as equilibrium constants; the free energy, enthalpy, and entropy changes of chemical reactions; activity coefficients; and the selective sensing of ions. The emphasis throughout is on understanding the foundations of the subject and how it may be used to study problems of chemical interest. The Primer is directed towards students in the early years of their university courses in chemistry and allied subjects; accordingly, the mathematical aspects of the subject have been minimized as far as is consistent with clarity.