Endoscopic ultrasonography (ES) enables accurate imaging of the layering structures of the gastrointestinal tract. The equipment is still evolving but has already reached a high degree of sophistication. The most relevant clinical indications are the analysis of submucosal tumors, the imaging of intestinal vascular anomalies, and, especially, the staging of gastrointestinal and biliopancreatic malignancy and the monitoring of the therapeutic efficacy of surgery, Nd:Yag laser photodestruction, and radiotherapy.