Anaplasmosis is a name for all tick-borne diseases caused by the bacteria of the Anaplasma genus. The genus, together with the Ehrlichia, Neorickettsia, Neoehrlichia, Wolbachia, Aegyptianelae and Xenohaliotis genera, belongs to the Anaplasmataceae family. In the last two decades, there has been a significant increase in tick-borne diseases both in humans and in animals. The increase is linked to global warming and the resultant increase in temperature and humidity, which contributed to the spread of the vectors that transmit Anaplasma and disease reservoirs of Anaplasma. Apart from that, there has also been an increase in human exposure to ticks due to more frequent trips into the countryside. This group of diseases is becoming a growing problem in veterinary and human medicine. Anaplasmoses include granulocytic anaplasmosis in cats and dogs, anaplasmosis in horses, and tick fever in cattle caused by the A. phagocytophilum species, cyclic thrombocytopenia in dogs caused by A. platys, as well as anaplasmosis in cattle caused by A. marginale. In addition to the aforementioned diseases in domestic animals, A. phagocytophilum is responsible for a disease in humans called human granulocytic anaplasmosis. Bacteria of the Anaplasma genus are pleomorphic obligate intercellular bacteria which parasitize different blood cells in mammals. There they reproduce using binary fission, and form typical inclusions called morulas within blood cells. A bite from an infected tick is the predominant cause of animal infection. The clinical picture depends on the type of bacteria causing the disease, but also on the type of the affected animal. Anaplasmoses are generally slow-course diseases characterized by non-specific symptoms and rarely animal deaths. Diagnosis is based on medical history, epizootiological data, and the clinical manifestation of the disease, as well as serological and molecular diagnostic methods coupled with microscopic findings of morulae. The diagnostic success varies depending on the choice of method, type of animal, and stage of disease. However, polymerase chain reaction is considered to be the most reliable diagnostic method. The medicines of choice for the treatment of anaplasmosis is tetracycline antibiotics, and improvement is visible shortly after beginning treatment. Since anaplasmoses are tick-borne diseases, prophylaxis should be directed at tick control. Vaccines for diseases caused by A. phagocytophilum and A. platys bacteria do not exist, while inactivated and attenuated vaccines may be used in cattle anaplasmosis prophylaxis.