Mycobacterium caprae, a member of the Mycobacterium tuberculosis complex, causes tuberculosis (TB) in man and animals. Some features distinguish M. caprae from its epidemiological twin, Mycobacterium bovis: M. caprae is evolutionarily older, accounts for a smaller burden of zoonotic TB and is not globally distributed, but primarily restricted to European countries. M. caprae occurs only in a low proportion of human TB cases and this proportion may even decrease, if progress toward eradication of animal TB in Europe continues. So why bother, if M. caprae is not an enigma for diagnostic TB tests and if resistance against first-line drugs is a rarity with M. caprae? This 'European' pathogen of zoonotic TB asks interesting questions regarding the definition of a species. The latter, seemingly only an academic question, particularly requires and challenges the collaboration between human and veterinary medicine.