This chapter is written in the question and answer format, which gives the description on the gastroenterology. Gastroenterology is a medical specialty that relates to the diagnosis of disorders related to the digestive system. Diseases affecting the gastrointestinal tract include the organs from mouth to anus, along the alimentary canal. Digestive disorders have become the most common medical problem. They can at most times be annoying, at times debilitating and in some cases, life-threatening. This chapter covers the symptomatology and evaluation of gastrointestinal disease, gastrointestinal bleeding, approach to diarrhea, diseases of the esophagus, diseases of the stomach and duodenum, diseases of the intestine, inflammatory bowel disease (IBD), probiotics and prebiotics, and miscellaneous. Constipation is defined as persistent, difficult, infrequent passage of hard stools, or seemingly incomplete defecation or evacuation. Many patients may also complain of excessive straining or lower abdominal fullness or discomfort. Upper gastrointestinal (UGI) bleeding is the bleeding proximal to the Duodeno-jejunal (esophagus, stomach, and duodenum) junction (ligament of Treitz). Inflammatory bowel disease (IBD) is an immune-mediated chronic intestinal condition. It results from inappropriate mucosal immune activation.