Glycogen, a branched polysaccharide of glucose, is the principal storage form of energy in animals and humans. This reagent-grade product is widely used in biochemical and pharmaceutical research as a standard for glycogen assays, in studies of carbohydrate metabolism, and as a component in cell culture media. It is stored in the liver and muscles, where it can be rapidly broken down into glucose to meet energy demands during physical activity or fasting. In the liver, it maintains blood glucose levels for vital organs like the brain. In muscles, it fuels contraction and movement. Glycogen is also explored in sports science for performance enhancement via carbohydrate loading and in medical research on disorders such as diabetes and glycogen storage diseases. As a specialty chemical, it serves as a niche additive in formulations for drug delivery and tissue engineering.