We reviewed published and unpublished written reports on bat mortality at wind farms in northwestern Europe. The estimated number of bats killed per turbine annually was relatively low (0–3) on flat, open farmland away from the coast, higher (2–5) in more complex agricultural landscapes, and highest (5–20) at the coast and on forested hills and ridges. The species killed almost exclusively (98%) belonged to a group (Nyctalus, Pipistrellus, Vespertilio and Eptesicus spp.) adapted for open-air foraging. The bats were killed by the moving rotor blades as they hunted insects attracted to the turbines. This occurred independently of sex and age. Peak mortality varied considerably in frequency and timing among years, but the events usually (90%) occurred on nights with low wind speeds in late July to early October and to a lesser extent (10%) also in April-June. The mortality increased with turbine tower height and rotor diameter but was independent of the distance from the ground to the lowest rotor point. It was also independent of the size of the wind park (1–18 turbines). Bat species other than the open-air suite referred to above are usually not at risk at wind turbines, because they fly below the rotors, but are still killed occasionally (2%).