Except for those organisms of medical, veterinary, or economic importance, there is a substantial lack of information of even the most basic biology of most species of coccidia. This is especially true for coccidian genera containing few species, since the majority infect vertebrates of little interest to most biologists. Life cycles of these “lesser coccidia” have traditionally been thought to be similar to species of Eimeria and Isospora. Recent studies, however, suggest a number of exceptions to our traditional concepts of apicomplexan biology. These studies have revealed some genera have exceptional development, e.g., Atoxoplasma, Calyptospora, Caryospora, Elleipsisoma, Frenkelia, Hammondia, and Neospora. The interest that these unusual apicomplexans have generated recently is typified by the fact that in the present book there are chapters on common coccidia, as well as chapters on more exotic coccidia, such as Caryospora spp. Although a number of fundamental questions still need to be answered concerning the basic biology of the genus Caryospora, enough information is now available to provide preliminary insights into this unusual, and perhaps heterologous taxon.