The genus Lasiopogon is a widespread group of robber flies inhabiting north temperate regions. This study is the first to examine the genus completely and to pay special attention to the genitalia, important structures in the taxonomy. Dr Cannings gives a cladistic overview of some defined species groups, and provides a detailed taxonomic and phylogenetic analysis of the 7 species groups and 29 species in the opaculus section. He describes 14 new species in this section and re-describes the others.