Concerns about global biodiversity are rising dramatically, yet we are lagging behind in the most basic prerequisite for its understanding and conservation: the inventory. Insect species may make up five or ten times the number of all other plant and animal species combined, and as such they represent one of the major challenges in biosystematic science. World Catalogue of Insects is an initiative aiming at compiling worldscale, authoritative catalogues of monophyletic insect taxa. We are therefore proud to launch this major series. Volumes will as a minimum contain standard nomenclatoral information on all names pertaining to the taxon treated, including type locality and distribution to the extent this is relevant. Additional information is optional, e. g., location, status and condition of types; biology; bibliographical information; pest status; vector status; etc. This volume one focuses on Hydraenidae (Coleoptera). (Series: World Catalogue of Insects)