Glycogen is a multibranched polysaccharide which serves as a part of energy storage in fungi and animals. In humans the glycogen is recognized and stored primarily in the cells of the liver and the muscles and functions as the secondary long-term energy storage with the basic energy stores being fats held in adipose tissue.

Glycogen is the analogue of starch a glucose polymer in plants and is more times explained to as animal starch, having a similar structure to amylopectin but more extensively branched and compact than starch. The Glycogen is establish in the form of granules in the cytosol or cytoplasm in various cell types and plays an significant role in the glucose cycle. Glycogen builds an energy reserve which can be fast mobilized to meet a sudden needed for glucose, but one which is less compact than the energy reserves of triglycerides.