Until recently, the system of classification of the Psylloidea was discussed exclusively on the basis of adult morphology. This volume follows the system proposed by Burckhardt. The terminalia of all species (m/f) have been figured, and the 5th instar nymphs of nearly all species have been keyed and figured. For each species, the distribution in and outside Denmark and Fennoscandia is briefly given. Information concerning the Scandinavian countries and on the biology of the species has been compiled from the literature and from the author"s observations, while distribution data for outside Fennoscandia and Denmark were derived mainly from Klimaszewski (1973).