Field investigations of the bat fauna were initiated with the use of ultrasound technique in 1978. Today we have an almost complete overview of bat distribution and species richness in Sweden and Denmark. Data were published as atlases, distribution maps, and facts on status for each species. Bats killed by wind turbines were discovered the first time in September 1999 on Gotland. Studies on behaviour of bats at turbines started in 2001 and were performed with the use of detectors, heat image cameras, acoustic playback experiments, and automatic registration. The research was funded by the Swedish Energy Agency, the Swedish Environmental Protection Agency (Vindval programme), the Swedish University of Agricultural Sciences, the Natural History Museum of Denmark, and the University of Copenhagen. The project on wind power at sea involved cooperation between scientists in Denmark, Germany and Sweden.