Endoscopy is the field of medicine that examines the inside of the body to diagnose, evaluate, and treat conditions of the esophagus (swallowing tube), stomach, and portions of the intestine. Endoscopy deals with examining the inside of the body using an endoscope, which is a device consisting of a flexible tube and an optical system. During an endoscopic procedure, an endoscope is introduced into the body through a natural opening. Endoscopic procedures can be used to diagnose and evaluate a condition and also as a form of treatment. The most common endoscopic procedures evaluate the esophagus (swallowing tube), stomach, and portions of the intestine.