The available textbooks on endoscopic ultrasound (EUS) typically focus on technique and interpretation of commonly observed images and scenarios and are aimed primarily at trainees. However, independent practitioners of EUS are often challenged by unusual cases which they are expected to handle competently despite the absence of authoritative guidance. The Diagnostic Endosonography aims to fill this gap by presenting carefully selected cases that will expand the practitioner’s knowledge base and cover important clinical challenges. The case material is organized principally according to anatomic site. Approximately 170 case reports are included, each of which is accompanied by an average of three to five high-quality EUS images; in addition, CT and PET scans are shown when appropriate. For each case, the case description is followed by helpful “teaching points” as well as up-to-date literature references and suggestions for future research.