This chapter are dedicated to theory of histopathology of digestive system. Coloured diagrams and pictures of histopathology of digestive system are given in detail. A brief write up about contents of chapter is given as introduction in the beginning of the chapter. Normal histology of digestive system is described initially with each topic to provide the basis for better understanding of histopathology. Histopathology of Esophagus, reflux esophagitis, Barrett esophagus, carcinoma esophagus, stomach, pyloric stenosis, gastritis, peptic ulcer, hyperplastic gastric polyp, gastric adenoma, carcinoid tumor, Meckel’s diverticulum, Gluten sensitive enteropathy, whipple disease, colitis, diverticulosis, acute appendicitis is described in detail with the help of 49 well illustrated diagrams.