The histological aspects of organs associated with GIT are shown in this chapter. The oesophagus on basis of structure is divided into mucosa, sub mucosa, muscularis externa and adventitial layer which are discussed with diagrams. The histology is correlated with associated clinical aspect. Relevant photomicrographs are given in atlas provided at the beginning of book. The histology of stomach and different parts of stomach are shown with suitable diagrams. The stomach is divided into pyloric and fundic parts. The small intestine is divided into duodenum, jejunum and ileum. All these show peculiar features as far there histology is concern. The characteristic features of above three are shown along with separate diagrams. Functional aspect of small intestine with relevant clinical associated with it are also given. Similarly concept of microanatomy of large intestine is also shown. The large intestine is divided into mucosa, submucosa, muscularis externa and serosal layers. Comparison of large intestine and small intestine are also tabulated. The different layers of appendix are same as that of large intestine but sub mucosa of appendix is largely occupied by infiltration of lymphatic follicles. Relevant photomicrographs are given in atlas provided at the beginning of book.