Covers all 309 species of the Sessiidae family presently known in the Palearctic region. The text represents the results of 10 years active research in the field and laboratory. It includes synonymic lists, a descriptive section, full data on male and female genitalia, bionomics, and habitat and distribution. Distribution maps for all species supplement the text. In all, 7 volumes are planned to accompany this first volume in the series.