The intracellular life-cycle of Eimeria are located in the host cell within a membrane-bound parasitophorous vacuole. The invasion process and the formation of the parasitophorous vacuole are mediated by characteristic organelles within the apical complex. During invasion, the parasitophorous-vacuole membrane is manipulated by the parasite and functions later in the development cycle as a molecular sieve, allowing the exchange of metabolites between parasite and host cell. Unlike the cyst-forming coccidia, there is little evidence of parasitophorous-vacuole membrane transformation in the later stages of the lifecycle of Eimeria species. Compared with the human pathogens Plasmodium and Toxoplasma, rather little is known about the parasitophorous vacuole and parasitophorous-vacuole membrane of animal pathogens of the genus Eimeria.