The suggestion for this collection of essays originated in part from a course given to graduate students at the University of Pennsylvania School of Medicine. In sections of this course, the conceptual developments in the fields of membrane transport and cellular respiration were traced to illustrate general aspects of the development of ideas in a scientific field. Discussions with peers on the topic also greatly enhanced the development of the project as it is reflected in this book. The volume reflects the breadth and scope of this rapidly developing field, and is an excellent treatise of a historical evaluation of how this field has developed.