These are exciting times for the diverse group of surgeons who perform craniomaxillofacial surgery. The AO/ASIF (Swiss Association of Internal Fixation) has played a crucial role in the growth of this field through its leadership in research, teaching, and cooperation with industry. As clinicians fascinated by the extraordinary progress in the field, the goal is to advance this new knowledge by teaching AO/ASIF courses and writing textbooks that supplement these courses and related workshops. This textbook adopts the case presentation format used in Craniomaxillofacial Fractures: Pr- ciples of Internal Fixation Using the AO/ASIF Technique. The breadth of the subject meant that a coeditor was advisable and, fortunately, Joachim Prein accepted that role. To make this a c- prehensive textbook, 75 international authorities wrote chapters in the areas of oral and m- illofacial surgery, plastic and reconstructive surgery, and otolaryngology and head and neck surgery. This textbook presents progress in craniomaxillofacial surgery through the technical and sci- tific advances in biomaterials, microvascular surgery, dental implantology, and surgical techniques. Section I covers basic considerations in the diagnosis of craniomaxillofacial defects and disorders.