Glycogen is a multi-branched polysaccharide that serves as the cellular energy storage in animals, fungi, and humans. In this book, the authors present research in the study of the structure, functions in the body and role in disease of glycogen. Topics discussed include the epidemiology, pathophysiology and genetics of Glycogen Storage Disease Type II (GSDII), glycogen metabolism during chronic liver diseases, muscle and liver glycogen in helminth-infected fish, and glycogen metabolism enzymes as molecular targets for drug development.