This book is an introduction for students and young doctors at the beginning of their career in diagnostic ultrasonography. It also presents the latest in innovations and techniques in gastrointestinal ultrasonography. The reader will find basic aspects of ultrasonography as well as highly advanced technical and research papers. The first category will be easy to understand for most readers. The second category may require some preparation from the student. All advanced papers represent the frontiers of knowledge.The first few chapters deal with the basic principles of ultrasound and its use in tissue characterization. They are followed by chapters on the use of ultrasound for the characterization of tissue biomechanics and on novel techniques such as 3D ultrasound and hydrosonography. The clinical applications are outlined in the last few chapters of the book.