Johne's disease is primarily an intestinal infection of ruminants. Largely ignored by the livestock industry in the past, Johne's disease has gained importance among producers because of the economic losses they incur from herd infections and the potential human health hazards associated with the causative agent Mycobacterium paratuberculosis. This study discusses the diagnosis, transmission, and control of Johne's disease; the impact of the disease on the food animal industry; and the possible impact on human health.