Endoscopic retrograde cholangiopancreatography (ERCP) is the standard approach to gaining access to the biliary and pancreatic ductal systems. However, in a small subset of cases anatomic constraints imposed by disease states or abnormal anatomy preclude ductal access via conventional ERCP. With the advent of endoscopic ultrasonography (EUS), with its unique capabilities of accurate imaging and ductal access via transmural puncture, there is now an alternative to surgical and percutaneous radiologic approaches in situations inaccessible to ERCP: endosonographic cholangiopancreatography (ESCP). This article reviews the background, technical details, published experience, and role of ESCP in clinical practice.