Ruminant infections by Anaplasma species are increasingly identified as significant and potentially fatal arthropodtransmitted diseases. Molecular diagnostic methods and epidemiological studies indicate that “anaplasma” infections are distributed in the whole world. Depending on the host and the bacterial species and bacterial strains symptoms vary from severe in sensitive animal to no sign in persistent infected animals. In Iran, five species including Anaplasma marginale, A. centrale, A. bovis, A. phagocytophilium and A. ovis are recognized in ruminants. Various factors have contributed to Anaplasma spp. detection in Iran including better consciousness by veterinarians; upgrade diagnostic tools and advanced techniques in molecular biology. The information about pathogen prevalence and genotypes and their vectors in different hosts and environments helps the foundation of surveillance and control programs for these pathogens. These findings may be used to create models to predict the risks of anaplasmosis and control, prevention, and treatment of disease.