Abstract: Hard ticks are haematophagous arthropods belonging to the family Ixodidae, and parasitize all classes of vertebrates in virtually all regions of the world. They do not have a significant direct pathogenic role in temperate regions, but in tropical zones they have an intensity of infestation that can induce anaemia with serious consequences. The main pathogenic role of hard ticks in Europe is associated with the transmission of viral, protozoal and bacterial agents that are pathogenic to both humans and animals. Hard ticks are intermittent ectoparasites that feed on a variety of vertebrate hosts, depending on their species and life cycle stage. Most species that parasitize ruminant species in France have triphasic life cycles and change hosts at each stage of their life cycles. Environmental factors mean that ticks alternate between periods of activity and of diapause. In France, the main diseases transmitted by ticks are bovine babesioses caused by Babesia divergens and to a lesser extent B. major, and anaplasmoses caused by Anaplasma phagocytophilum (ehrlichiosis) and A. marginale. Five species of hard ticks parasitize ruminants in metropolitan France. Each species is associated with a particular biotope which determines its geographical distribution. Ixodes ricinus is the most common, and is the vector for B. divergens, A. marginale, A. phagocytophilum, Borrelia burgdorferi and Coxiella burnetii. Dermacentor marginatus lives primarily in forest areas and is absent from artificial environments. Dermacentor reticulatus is active in more humid and colder seasons than D. marginatus, and is particularly common in Normandy, central France and the South West of France. D. reticulatus is the vector for equine and canine babesioses and is involved in the transmission of Francisellatularensis. Rhipicephalus bursa is very adaptable and has similar ecological requirements to D. marginatus, although it prefers sub-Mediterranean biotopes. R. bursa is involved in the transmission of Babesia caballi, Theileria equi and Babesia ovis. Haemaphysalis punctata is the vector for B. major. Species of tropical origin are also occasionally found in France due to accidental imports.