Injury to the posteromedial corner (PMC) of the knee differs anatomically and biomechanically from isolated injury to themedial collateral ligament. Newer anatomic and biomechanical studies are refining the field's understanding of the medial sideof the knee, as well as its role in multiple ligament injuries. Valgus instability places additional strain on a reconstructed anterior or posterior cruciate ligament, which can contribute to late graft failure. Injuries to the PMC may not heal without surgical repair or reconstruction, particularly when part of a multiple-ligament injury. Identification of PMC injury before cruciate reconstruction is important so that appropriate repair or reconstruction of the PMC and medial collateral ligament can be undertaken at the same time. This article reviews the relevant literature on the PMC, discusses reasons for selective operativemanagement, and illustrates reconstructive strategies for PMC injuries occurring as part of a medial-sided or multiligament injury to the knee.