Navigation systems for operative assistance in knee joint surgery have been established in the last 5 years. Among the large number of variable systems, the image-free kinematic systems have won widespread acceptance. The C-arm based systems are not superior to the image-free systems. The CT-based systems are advantageous in completely destroyed joints (with marked joint erosion) or advanced congenital or traumatic deformities. The intraoperatively-performed Iso-C (3D) technique presents data sets in CT-quality, but because of its small data volume currently is limited to the reconstruction of articular surfaces following fractures. The use of image-free navigation in resurfacing knee arthroplasty is in the meantime beyond controversy whereby deviations in the mechanical axis from normal values can be significantly reduced. For high tibial osteotomies navigation modules will be soon available for marketing. However, with these modules, intraoperative imaging is indispensable, but it will be image-free in the future. The early clinical results are promising. Cruciate ligament navigation is not yet a clinical standard be-cause of the considerable associated time expenditure. The appropriate modules are still under development.