Although optokinetic nystagmus was described as a clinical phenomenon over 150 years ago, its neurophysiologic mechanism has provoked ongoing controversies and enthusiasm for its clinical application has been sporadic and tepid. In the past 15 years, improvements in clinical and experimental oculography, neuroanatomy, and single unit neuron recordings in alert animals have helped to resolve the neural circuitry of optokinetic nystagmus and to better define its clinical usefulness. The writer reviews the history of the experimental study of optokinetic nystagmus and the clinical circumstances in which this office test may be of particular value.