There are currently 1590 terrestrial arthropod species identified as alien to Europe. Of these, 513 are predators or parasites. The largest group is the insects (409 species), followed by spiders (47 species), myriapods (34 species) and mites (23 species). The species within these alien groupings are extremely diverse, as highlighted by the large number of families represented (115 families). The majority (66.1%) of alien arthropod predator and parasite species arrived unintentionally, but at least 174 (33.9%) have been introduced intentionally, mainly for biological control purposes. Assessment of the major invasion pathways is difficult due to the lack of comprehensive information but it is likely that the majority of predatory or parasitic alien arthropods arrive through leading-edge dispersal or as contaminants and stowaways. The number of new species arriving in Europe has progressively increased since 1500, with the increase in global trade over the last century accelerating this rate of increase. Only a small number of alien predatory and parasitic arthropods in Europe have been shown to cause either an ecological or economical impact, yet knowledge is severely limited by a paucity of data.