Knee injuries continue to present a complex set of clinical problems. The answers to these problems have recently been redefined by the application of sophisticated biomechanical research methods to the study of knee ligaments and joint function. This manuscript reviews contributions which our laboratory has made to the understanding of knee injury, highlighting those research findings which form the basis for our clinical treatment of knee ligament injuries. High strain-rate techniques for studying knee ligament failure have replaced the previous low strain-rate methods and distinguish the failure mechanism of ligaments from that of bone. Ligament function is now further defined by measuring the restraining force provided by specific ligaments, adding to the information provided by cutting studies. The development of the 6-degrees-of-freedom concept and the instrumented kinematic chain now permit precise analysis of joint position, motion, and laxity. Biomechanical evaluation of intra-articular anterior cruciate ligament substitution has emphasized the importance of selection of a high-strength graft material, meticulous surgical technique with attention to graft vascularity, precise location of graft fixation sites, judicious adjustment of graft tension, post-operative protection during tissue remodelling, and a carefully conceived rehabilitation program. Newer biomechanical research methods have provided a sound scientific foundation on which to base clinical decisions concerning the care of knee ligament injuries.