Computer Graphics came into the medical world essentially after the arrival of 3D medical imaging. Graphics techniques are already integrated in the diagnosis procedure by means of the visual three- dimensional analysis of static computer tomography, magnetic resonance and even ultrasound data. Many scientists believe that the representations these techniques provide should no longer remain static pictures of the patients'' body. The next step in computer assisted diagnosis and surgery planning depends on the development of functional 3D models of human body, which are dynamic. This book steps in this direction as it proposes a model of articulations based on biomechanical information. Such model is able to simulate the joint functionality in order to allow for a number of medical applications, as diagnosis and surgery planning. The book discusses the requirements for such models, which includes efficiency to allow smooth interaction and realism for medical accuracy. A combination of kinematical motion for the rigid parts, such as bones, and physical simulation of the soft tissues is presented as the key element.