This volume deals with the European species of the family Sepsidae, a small family of acalyptrate flies. The taxonomy, biology and faunistics of all the European species are revised with emphasis on the Fennoscandian species, and the detailed distribution of the species known from Fennoscandia, the adjacent areas of Russia, Germany and Great Britain is tabulated in a catalogue. Keys are given to generic level for eggs, larvae and adults, and to species for the adults. Descriptions of the adults are provided for genera and species, together with diagnostic notes on the immature stages. The distribution and biology of the European species is summarized, and the results of extensive type-studies are presented. Illustrations are given of the male fore legs and genitalia of all the European species, and also of other characters of diagnostic importance for the egg, larval and adult stages. Nine genera and 44 species are dealt with, and one new species is described.