Endoscopic ultrasound (EUS), a relatively new addition to the endoscopist’s diagnostic armamentarium, provides detailed images of the gut wall layers and surrounding organs. Endosonography is highly accurate in the staging of gastrointestinal neoplasms and may provide information that is invaluable in treatment planning, such as evidence of unresectability. EUS also has particular utility in the evaluation of submucosal lesions of the gastrointstinal tract and the preoperative localization of pancreatic endocrine tumors. Currently, in the United States, Olympus and Pentax manufacture two different endosonography systems, each with unique advantages and disadvantages. Recently, EUS-directed biopsy has enhanced the diagnostic potential of the procedure. With the recent approvel of CPT codes and reimbursement values, interest in the procedure is likely to expand. Adequate training in EUS is essential for the successful performance of the procedure; a period of proctored training with an experienced endosonographer is recommended.