Technical Abstract: The chapter "Lactose: Chemical and Physicochemical Properties" for the reference textbook "Developments in Dairy Chemistry - 3 - Lactose and Minor Constituents" has been revised and updated. Topics covered include occurrence, biosynthesis, physical properties, chemical reactions, applications, nutritional and physiological effects, and uses. The Chapter is intended as source material for those interested in a definitive review of the physical and chemical properties of lactose.