Coccidiosis in ruminants results from complex interactions between hosts and parasites with many external factors influencing the severity of disease. The study of ruminant coccidiosis is still very much in its infancy despite the advances made in recent years in determining life cycles, pathogenesis, epidemiology and control. Many of the life cycles of the species, considered to be of lesser importance, have still to be elucidated and controversy still exists concerning the pathogenicity of some of these species. Outbreaks of coccidiosis occur with ever increasing frequency yet few drugs exist for prevention. Only limited investigations have been undertaken on immunological methods of control. This paper seeks to review the current knowledge on the biology and control of the coccidial species affecting cattle, sheep and goats.