Of the 19,400 native species and 125 families forming the European diptera fauna, 98 species (less than 0.5%) in 22 families are alien to Europe. Th ese aliens constitute 66 species (18 families) of the suborder Brachycera and 32 species (4 families) of the suborder Nematocera. By family in this category, there are 23 Cecidomyiidae species, 18 Drosophilidae, nine Phoridae, eight Tachinidae and seven Culicidae. Another 32 fl y species belonging to fi ve families are considered to be alien in Europe. Th ese invasives native to other European countries are composed of 14 species of Cecidomyiidae, seven Syrphidae, fi ve Culicidae and three species each of Anthomyiidae and Tephritidae. Th e date of the fi rst record in Europe is known for 84 alien species. Arrivals of alien species of Diptera have accelerated rapidly since the second half of the 20 th century. North America appears to be the dominant contributor of the alien fl ies. Th e majority of alien Diptera were introduced into or within Europe unintentionally, with only three predators released intentionally for biological control. Alien Diptera are predominantly phytophagous (35.6%), while a lesser portion are zoophagous (28.6%) or detrivorous /mycetophagous (29.6%). Ecological impacts on native fauna and fl ora have not been documented for any of the alien species established in Europe. However, 14 alien species have economic impacts on crops.