Postoperative knee stiffness after anterior cruciate ligament reconstruction surgery is a significant clinical problem. Clinical deficits of knee flexion more than 10 degrees can limit function and athletic performance, and extension deficits of more than 5 degrees can cause gait changes and altered knee kinematics. The incidence reported in the literature varies significantly. Risk factors for the development of this condition include technical factors, graft selection issues, the timing of surgery relative to the traumatic injury, the presence of associated injuries, and postoperative rehabilitation. This chapter will review the incidence, risk factors, pathology, prevention, treatment options, and the clinical results of management of this condition.