Since its first description in dogs in 1984, the protozoan parasite Neospora caninum has been found to infect a wide range of animals, worldwide. In cattle, N. caninum has particular significance as a cause of abortion in which persistence of infection in the mother, recrudescence of the parasite during pregnancy, and the vulnerability of the placenta and foetus to invasion are important features. This article discusses how Neospora invades cells, how it infects and causes disease in several animal species, and particularly how it has evolved a special niche in cattle and dogs that ensures its survival.