Casein from bovine milk is a phosphoprotein. It make up approximately 80% of the total protein in bovine milk. It is proposed to be the main protective constituent in milk.

It has a wide variety of uses, from being a major component of cheese, to use as a food additive, to a binder for safety matches. As a food source, casein supplies amino acids; carbohydrates; and two inorganic elements, calcium and phosphorus.