Within the past decade, knowledge of knee ligament injuries, although far from being complete, has increased significantly. The development of new clinical tests has enabled the clinician to make more accurate diagnoses of both the acutely and chronically injured knee and has led to the recognition of the importance of injury to the anterior cruciate ligament, posterior cruciate ligament, and the posterolateral capsule. These tests have also helped to differentiate medial collateral ligament and other combined ligament injuries from the “isolated” medial collateral ligament injury, allowing for non-operative treatment of the latter. The reported natural history studies of those with anterior or posterior cruciate ligament deficiency have helped to define our indications for surgery better. The less than satisfactory long-term outcomes of primary repair of anterior cruciate ligament injuries have resulted in more refined surgical techniques of repair and to the concept of repair and tendon augmentation. The reports that those with severe functional instability have a high probability of developing significant early traumatic arthritis have led to a more aggressive surgical approach. The short-term results of a number of different procedures have been encouraging. Advances in the field of sports science have had significant impact in the treatment of knee ligament injuries. The recent development of sophisticated knee testing devices will facilitate better evaluation of the biomechanical stability of the knee joint after reconstructive procedures and for comparisons between these procedures. More detailed knowledge of the adverse changes that occur in muscle has led to the concept of early functional rehabilitation in order to limit the deleterious effect that immobilization has on muscle, ligament, and articular cartilage.