In 1979 Dr Sperelakis published the `Origin of the Cardiac Resting Potential' in the Handbook of Physiology of the Heart . Since that time, many investigators and teachers of membrane biophysics have used this article as a source of reference on the fundamental principles and equations describing the factors that establish the resting potential in excitable and non-excitable cells. Professor Sperelakis has expanded the scope of this article to provide the present book, creating a comprehensive work and an invaluable reference on the electrophysiological concepts underlying cellular excitability. There has long been a need for a text which precisely defines the assumptions underlying the derivations and equations that describe the principles of electrical excitability and maintenance of ion gradients in excitable cells. Here, Professor Sperelakis not only defines the equations and underlying concepts of membrane potentials, but gives working examples of solutions, thus allowing investigators to utilize the fundamental principles in their research, and students of membrane physiology to establish a sound basis of electrophysiological theory. ` I have used the `Origin of the Cardiac Resting Potential' in graduate courses on cell physiology and biophysics, and look forward to using this new book. The time and effort required to put this work together reflects the dedication of Dr Sperelakis to the field of membrane biophysics and electrophysiology in his long, productive career. ' From the Foreword by Dr David R. Harder.