Common buckthorn, Rhamnus cathartica, and glossy buckthorn, Frangula alnus are Eurasian shrub species that are invading a number of habitat types in the northeast and north-central regions of the United States and Canada. Both species are very adaptable, forming dense thickets that inhibit the growth of native plants, and both species are also alternate hosts for the fungus that causes oat rust disease. In 2001, research was initiated to determine if there are suitable biological control agents for these two buckthorn species. Early research efforts focused on identifying insects species associated with the buckthorn species in its native range followed by preliminary host specificity testing of key species. Over a three year period, field surveys were carried out in over 80 buckthorn sites in Europe and more than 900 insects samples have been collected. The community of specialized arthropods associated with R. cathartica and F. alnus in Europe is largely dominated by Lepidoptera (22 species), followed by Hemiptera (6 species), Diptera (4 species), Coleoptera (1 species) and mites (2 species). The complex of specialized arthropods is much higher on R. cathartica than on F. alnus. Preliminary host range studies with several insect species match with host preferences observed in the field. Arthropod species that attacked both R. cathartica and F. alnus in their native range will likely attack native North American species in both genera. Future research will focus on host specificity of specialized defoliators, internal and seed feeders, as well as gall inducing arthropods identified in the surveys.