Collagen is a large protein molecule that is responsible for the structure of skin, ligaments, bones, cartilage, and has been widely used in leather, glue, gelatin. In recent years, it has also been used as an ingredient of drinks, cosmetics, and pharmaceutical products.This book shows various fields of collagen, such as its structure, physical properties, chemical properties, functions in the living body, digestion and absorption, related diseases, and various industrial uses.