The taxonomy of the heteroxenous apicomplexan protozoan genus Sarcocystis was reviewed, and a list of 122 species with their synonyms and hosts given. Both definitive and intermediate hosts are known for only 56 species. The fine structure of the sarcocyst wall may change with age and is not considered necessarily satisfactory for separating species. Specificity for the intermediate host is not narrow for all species. Earlier work on transmission of the parasite from one intermediate host to another should be repeated in the light of present knowledge of the life cycle of species of Sarcocystis.