Kinematics is the description in terms of relative motion between two rigid bodies. The knee joint is the largest in the human body and certainly one of the most complex, both from an anatomical and functional point of view, and thus its kinematics have involved researchers for a long time. In 1983, Grood and Suntay presented a joint coordinate system for the description of the three-dimensional rotational and translational motion between two rigid bodies, and they applied this system to the knee joint. A fundamental role in the kinematic analysis of the joints is played by motion capture systems; in fact, using certain experimental setups are obtained the coordinates of the markers which will be used to calculate, in the case of the knee, joint rotations and clinical translations.