The posterolateral corner (PLC) of the knee is a critical element for a functional lower extremity. It consists of an array of complex ligamentous and musculotendinous structures. The primary function of the PLC is to resist varus and external rotation and posterior translation of the tibia. Injuries to these structures can cause significant disability and compromise activities of daily living and work, recreational, and sporting activities. A thorough understanding of the complex anatomy and biomechanics of the PLC will aid the clinician in this challenging diagnostic and therapeutic problem. The first section of this paper describes the anatomy of the PLC of the knee focusing on the intricate insertion sites of the individual structures. The second section discusses how the anatomy influences the biomechanics of the PLC.