Aquatic insects species in North Europe are found in ten different orders, representing a wide variety of form and life styles. Most diverse are the dipterans, the two-winged flies and midges, including among others the notorious blood-sucking pests of the boreal and subarctic regions. Other diverse orders are chiefly the beetles and caddisflies, including several hundreds of species occupying most of the available freshwater environments. Besides the aquatic beetles and bugs, insects classified as aquatic normally develop in water, whereas the adult flying forms are terrestrial. Swarming mayflies and hovering libellulas are well-known characteristics of lake and stream shores. Insect larvae are nowadays widely used in environmental monitoring, with actual species composition at a locality providing reliable evidence on the impacts of acidification and pollution. Environmental applications have engaged many people in the identification of aquatic insect larvae, on scientific, commercial, or governmental basis. However, these activities have been hampered by a general lack of an up-to-date standard work providing modern nomenclature and reliable identification keys including all known taxa from the region. This CD-ROM format which contains both Volume 1 and Volume 2 of the printed editions of Aquatic Insects of North Europe, published in 1996 and 1997 with a total of 714 pages and 3426 line drawings is designed to fill a taxonomic knowledge gap. The information provided focuses geographically on the Nordic Countries Denmark, Norway, Sweden, and Finland. Aquatic Insects of North Europe is a rich source of information on natural history, morphology, faunistics, classification, and identification.