Mark Hallett, M.D., is chief of the Human Motor Control Section at the National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health. His research focuses on the physiology of human movement and movement disorders. He is currently editor in chief of Clinical Neurophysiology and an associate editor of Brain. He was the clinical director of NINDS until July 2000 and is past president of the American Association of Neuromuscular and Electrodiagnostic Medicine and the Movement Disorder Society and past vice president of the American Academy of Neurology. He can be reached at firstname.lastname@example.org.