A revision of the European species of Siphona Meigen (1803) is presented. New diagnostic characters, especially based on structural differences in the male and female genitalia, are introduced. Also the traditionally used characters are revised. Four species are described as new: ingerae, mesnili and variutu from Denmark, and martini from Sweden. Thirteen other species are diagnosed. All seventeen species are keyed, and details of the genitalia are illustrated. Two lectotypes are designated. Notes on the affinities and distribution of the species are given. The biology is reviewed and possible host-parasite relationships are presented in an annotated list. True aerial swarming (synorchesia) of male Tachinidae is reported for the first time.