Proteins are polymers of amino acids. The properties of the individual amino acids, as well as the proteins themselves, that occur in food interest food chemists. The amino acid composition influences the nutritional value of individual proteins and entire diets. The amino acid sequence of particular proteins defines their three-dimensional structure and biological function. The properties of many food materials are derived from the structures of the original plant or animal tissue and their component proteins. The special character of milk's casein proteins explains milk's function as a vehicle of phosphate, calcium, and protein as well as cheese formation. Egg white is valued as a food ingredient for the stable foams its proteins form. Muscle tissue (of mammals, fish and birds) undergoes a complex sequence of post-mortem changes essential for desirable texture etc. Changes in the muscle pigment myoglobin involving free radicals can be related to other quality parameters. Collagen, the key protein of connective tissue, toughens with age but can be extracted to give gelatin, a valued gelling agent. Bread dough's viscoelasticity is explained in terms of the molecular properties of the storage proteins of cereal grains, the gliadins and glutenins that form gluten. The genetic basis of baking performance is explained. The chapter concludes with a list of specialist books and review articles for further study.