Instability following total knee arthroplasty is one of the major causes of revision surgery. In most cases, it can be prevented by using an appropriate prosthesis and a good surgical technique. Particular attention should be given to confirmation of diagnosis for which thorough history taking, complete physical examination and radiographic evaluation are needed. With regard to treatment, identification of the etiology of instability is crucial for establishing proper treatment plans; instability would persist without correction of the cause of the initial instability. For successful revision surgery, balanced medio-lateral and flexion-extension gaps should be achieved. Constrained or rotating-hinge total knee prosthesis should also be considered as an alternative option for certain subsets of patients with instability.