Glycogen is a complex carbohydrate that serves as a form of energy storage in animals and fungi. It is primarily found in the liver and muscles, where it can be quickly converted into glucose when the body needs energy. Glycogen is made up of long chains of glucose molecules, making it a highly efficient way to store energy. When the body requires energy, such as during exercise or fasting, glycogen is broken down through a process called glycogenolysis. This process releases glucose into the bloodstream, providing a readily available source of energy for cells. Maintaining proper glycogen levels is important for overall health and athletic performance.