Trypsin is a serine protease in the digestive system of humans and animals. This book presents current research in the structure, biosynthesis and functions of trypsin. Topics include the study of trypsins from submammalian vertebrates with special emphasis on fish; the applications of trypsin in food processing; trypsin acting as an activating enzyme in gut innate immunity and protease-activated receptor 2 in the enteric nervous system.