The Eucoccidiorida are an order of microscopic, spore-forming, single-celled parasites belonging to the apicomplexan class Conoidasida.

Among these parasites are the Toxoplasma gondii that cause toxoplasmosis and Isospora belli, which results in isosporiasis.

This is the largest order in the class Conoidasida and contains those species that all undergo merogony (asexual), gametogony (sexual) and sporogony (spore formation) during their lifecycles.

The genera include: Adelea, Adelina, Alveocystis, Atoxoplasma, Babesiosoma, Barrouxia, Bartazoon, Besnoitia, Calyptospora, Caryospora, Caryotropha, Chagasella, Choleoeimeria, Cryptosporidium, Crystallospora, Cyclospora, Cyrilia, Cystoisospora, Dactylosoma, Desseria, Diaspora, Dorisa, Dorisiella, Eimeria, Elleipsisoma, Epieimeria, Frenkelia, Ganapatiella, Gibbsia, Goussia, Gousseffia, Grasseella, Hammondia, Haemogregarina, Hemolivia, Hepatozoon, Heydornia, Hoarella, Hyaloklossia, Isospora, Ithania, Karyolysus, Klossia, Klossiella, Lankesterella, Legerella, Mantonella, Nephroisospora, Neospora, Octosporella, Orcheobius, Ovivora, Pfeifferinella, Polysporella, Pseudoklossia, Pythonella, Rasajeyna, Sarcocystis, Schellackia, Selenococcidium, Selysina, Sivatoshella, Skrjabinella, Spirocystis, Toxoplasma, Tyzzeria, Wenyonella Among the heteroxenous and cyst-forming genera are: Besnoitia, Cystoisospora, Frenkelia, Hammondia, Neospora, Sarcocystis, and Toxoplasma.

Two major clades have been identified: the isosporoid coccidia (Toxoplasma, Neospora, Isospora [in part], and Sarcocystis) and a second clade containing Lankesterella, Caryospora and the eimeriid coccidia (Cyclospora, Isospora [in part] and Eimeria).