Since acute surgical repair is vastly superior to any form of reconstructive procedure available, it is extremely important that acute ligamentous injuries of the knee do not go unrecognized. Chronic symptomatic instability after untreated major ligament injury marks "the beginning of the end' for the knee, and reconstruction is indicated. The classical stress tests for knee ligament disruption are generally reliable, and the interested doctor should have little difficulty in accurately diagnosing and classifying acute injuries or chronic instability. The technique of examination and classification of knee instability is described. The techniques of acute repair, as well as of selected reconstructive procedures, are described. Reconstruction for anteromedial subluxation is confined to advancement of the medial collateral ligament and posteromedial capsule as a single cuff, moving its tibial attachment distally and anteriorly. Fascia lata reconstruction is used for repair of anterolateral subluxation. Both these extra-articular anterior reconstructions can, in severe cases, be improved by the addition of a midline procedure, using the patellar tendon as an intra-articular graft. Transfer of the medial head of the gastrocnemius muscle is used for symptomatic posterior subluxation.