This chapter entails study of diseases involving GI tract and the hepatobiliary tree. This is one of the regularly quizzed specialties on Boards. There are always several questions regarding GERD, PUD, GI Bleed and IBD. Therefore special attention has been paid at ample coverage of these topics. Notable topics of Gastroenterology are Achalasia, Esophageal carcinoma, Esophagitis, Mallory-Weiss Syndrome, Boerhaave syndrome, GERD, Barret’s, Peptic ulcer disease, Zollinger-Ellison Syndrome, Inflammatory Bowel Disease, Irritable Bowel Syndrome, Carcinoid syndrome, Colon cancer, Polyposis, Gastrointestinal bleeding, Lactose intolerance, Celiac Disease, Tropical Sprue, Whipple Disease, Diverticulosis and Diverticulitis, Acute and Chronic Pancreatitis, Alcoholic Liver Disease, Biliary Sclerosis, Sclerosing Cholangitis, Hemochromatosis, Wilson’s Disease. Few of the quick reference tools in this chapter include Dysphagia differential and associated conditions, Achalasia and Esophageal Carcinoma differentiation, Esophageal dysmotility diseases, Differential of Diarrhea.