Babesiosis is the disease caused by infection of the erythrocytes of mammals by Babesia species, which are Apicomplexa protozoa belonging to the suborder Piroplasmidea and the family Babesiidae. They are different from the Theileriidae, which can also infect white blood cells and endothelial cells. Babesiosis is one of the most important tick-borne infectious diseases of domestic and wild mammals and still poses significant diagnostic and therapeutic challenges for veterinary practitioners around the world. It is an increasing problem worldwide because of the expansion of tick habitats and the increased mobility of animals, which promote the spread of parasites into new geographical areas. Babesia species can, exceptionally, infect humans, especially splenectomised or immunocompromised individuals. The majority of human cases involve B. microti, a parasite of rodents, but human infections may also be caused by B. divergens, which infects cattle, or by Babesia related to B. odocoilei, which infect cervids. The majority of new developments, in regard to taxonomy, epidemiology, pathogenesis and control, concern canine babesiosis, whereas piroplasmosis in horses or cattle retains the classical description, therefore the focus of this article will be on infection in dogs.