Computer assisted surgery is a relatively new development in maxillo-facial surgery which has been in use approximately since the beginning of the Millennium. It can be applied pre-, intra- or postoperatively. Preoperatively it is utilized for instance for visualizing pathologies, virtual planning of fracture repair in 3D, simulation of fracture repair and planning of tumour resections and reconstruction. Modern computer technology also allows three-dimensional visualization and planning of orthognathic surgery. Some software products even integrate 3D portrait photographies of patients and permit a realistic simulation of the postoperative changes of facial soft tissue after osteotomies of the maxilla and the mandible. Ideally, these simulations reproduce the exact outcome of surgery. Intraoperatively the predominant use of computer assisted surgery is navigation guidance for a number of different interventions, mostly for primary or secondary trauma repair. Postoperatively computer assisted imaging helps to better evaluate and visualize surgical results. This thesis gives an overview of the evolution of primarily two topics: computer assisted trauma repair and realistic orthognathic soft tissue simulation. Today, the first subject has become a daily routine application. It improves surgical outcome and patient safety. Soft tissue simulation after orthognathic surgery however is not yet ready to be used routinely.