Endoscopic ultrasound (EUS) was introduced in the early 1980s in an attempt to improve sonographic imaging of the pancreas. Its uses have been expanded to include examination of the upper and lower gastrointestinal tracts, hepatobiliary and portal systems,and the anal sphincter; diagnosis and staging of esophageal, gastric,and pancreaticobiliary tumors; and evaluation of mediastinal nodes in lung cancer. Although EUS has its limitations and is greatly dependent on operator skill, it has wide-ranging interventional and therapeutic applications that can be expected to increase in the future with technologic advances and greater educational opportunities for physicians.