A total of 383 alien insect species were registered in the Czech Republic, which represents 1.4% of local fauna. The most numerous taxonomic groups are Homoptera (116 species, 30.3%), Coleoptera (110; 28.7%) and Lepidoptera (37; 9.7%). The occurrence of 200 species (52.2%) are limited to closed heated spaces, casual aliens (28; 7.3%) infiltrate the outdoor environment for a short term only, 36 (9.4%) naturalized non-invasive species do not spread from the location of introduction, 50 (13.1%) species are post-invasive and 69 (18.0%) invasive. From the species registered, 61 (15.9%) are stored product pests (especially Coleoptera 36 species, Psocoptera 11, and Lepidoptera 9), 50 (13.1%) are plant pests indoors (especially Coccinea 33 species, Aphidinea 7, and Thysanoptera 6), 25 (i.e. 6.5% of aliens) are pests in agriculture, forestry, and in ornamental cultures, 15 species (3.9%) are important animal parasites, and 5 species (1.3%) can affect biodiversity. Of the remaining 227 species (59.3%), no economic or ecological effects were found. The origin of most of the species living eusynanthropically is in the tropics and subtropics; of the 155 naturalized (non-invasive, post-invasive, and invasive) species, 42 (27.1%) originate from the Mediterranean, 36 (23.2%) from North America, 28 (18.1%) from Central to Southwest Asia, 14 (9.0%) from East Asia, 13 (8.4%) from South and Southeast Asia, with the remaining 22 species (14.2%) coming from other areas.