Endoscopic ultrasound (EUS) was developed in the 1980s to address, in part, the limitations of transabdominal ultrasound imaging of the abdomen. Adequate ultrasonography relies on the transmission of sound waves. Thus imaging of the abdomen by external ultrasonography is limited by interference of bowel gas. Endoscopic ultrasound reduces bowel gas interference by placing the ultrasound transducer directly within the gastrointestinal lumen via endoscopy. Thus, merging the technologies of endoscopy and ultrasonography allows the trained endosonographer to obtain detailed images of the pancreas, among many other uses. Endoscopic ultrasound is generally performed in an endoscopy facility with the availability of skilled nurses or technicians, sedation and appropriate endoscopic equipment (Figure 8.1) . Upper EUS is routinely performed after an overnight fast and is most often completed in the outpatient setting. Patients are placed under intravenous conscious sedation or monitored anesthesia care, and the procedure is completed in 30–60 minutes, depending on the complexity of the examination. Endoscopic ultrasound accuracy is dependent on a number of factors including the quality of available equipment, operator experience in technique and interpretation, and patient anatomy and body habitus. There is a recognized learning curve for the performance of accurate EUS examinations and, as with standard ultrasonography, accuracy improves with increased experience . Endoscopic ultrasound imaging of the pancreas can be performed via either radial or linear echoendoscopes (Figure 8.2). Radial echoendoscopes provide a complete, 360-degree image perpendicular to the axis of the endoscope.