Parkinson disease is a progressive neurodegenerative disorder characterized by a variety of motor and nonmotor features. This article reviews the problems of postural instability and gait disturbance in persons with Parkinson disease through the discussion of (1) the neuropathology of parkinsonian motor deficits, (2) behavioral manifestations of gait and postural abnormalities observed in persons with Parkinson disease, and (3) pharmacologic, surgical, and physical therapy–based interventions to combat postural instability and gait disturbance. This article advances the treatment of postural instability and gait disturbance by condensing up-to-date knowledge and making it available to clinicians and rehabilitation professionals.