Knee joint is the largest and the most complex joint in the body. It serves the dual functions of weight bearing and locomotion. Knee joint is generally referred to be a modified, synovial hinge type of joint as it permits rotational movement. The main articulation of the knee is formed between the condyles of femur and tibia i.e. tibiofemoral joint, which is actually the knee joint proper, however, the other joint is also formed between femur and patella, i.e. patellofemoral joint within the single joint cavity. Since the knee is a modified hinge joint, rotation in flexed knee also takes place apart from flexion-extension movements. Flexion or bending of the leg occurs at the knee so that the posterior surface of the leg comes in contact to the posterior surface of thigh. Extension is the reverse movement from the flexed knee, or it is the straightening of leg at the knee. A detailed discussion on the muscles of knee are has been given in this chapter.