A detailed review is presented of the history, geographical distribution, cause, epidemiology, clinical features, pathogenesis, pathology, diagnosis, prevention, control and economic effects of scrapie in sheep. Brief mention is made of the disease in goats and moufflon. The nature of the agent causing scrapie, the genetic control of the incubation period in sheep and the natural transmission of scrapie in sheep and goats are discussed. National efforts to control scrapie in various countries are outlined.