Postoperative stiffness is a debilitating complication of total knee arthroplasty. Preoperative risk factors include limited range of motion, underlying diagnosis, and history of prior surgery. Intraoperative factors include improper flexion-extension gap balancing, oversizing or malpositioning of components, inadequate femoral or tibial resection, excessive joint line elevation, creation of an anterior tibial slope, and inadequate resection of posterior osteophytes. Postoperative factors include poor patient motivation, arthrofibrosis, infection, complex regional pain syndrome, and heterotopic ossification. The first steps in treating stiffness are mobilizing the patient and instituting physical therapy. If these interventions fail, options include manipulation, lysis of adhesions, and revision arthroplasty. Closed manipulation is most successful within the first 3 months after total knee arthroplasty. Arthroscopic or modified open lysis of adhesions can be considered after 3 months. Revision arthroplasty is preferred for stiffness from malpositioned or oversized components. Patients who initially achieve adequate range of motion (>90 degrees of flexion) but subsequently develop stiffness more than 3 months after surgery should be assessed for intrinsic as well as extrinsic causes.