A first attempt is made to revise the European species of the gall midge genus Planetella Westwood, 1840 (Diptera: Cecidomyiidae), with a focus on the fauna of the Czech Republic, Slovakia and Denmark. A total of 19 species are recognized based on unique DNA sequences, of which 13 are described as new to science: Planetella adami Ševčík & Hippa sp. nov., P. aestivalis Ševčík & Hippa sp. nov., P. antennata Ševčík & Hippa sp. nov., P. atrobrunnea Ševčík & Hippa sp. nov., P. attilai Ševčík & Hippa sp. nov., P. csabai Ševčík & Hippa sp. nov., P. davidi Ševčík & Hippa sp. nov., P. galiciensis Ševčík & Hippa sp. nov., P. hlisnikovskyi Ševčík & Hippa sp. nov., P. muranica Ševčík & Hippa sp. nov., P. riparia Ševčík & Hippa sp. nov., P. submontana Ševčík & Hippa sp. nov., and P. thermophila Ševčík & Hippa sp. nov. Four previously described species are recognized in the collected material: Planetella arenariae (Rübsaamen, 1899b), P. fasciata (Meigen, 1818) sp. restit., P. gallarum (Rübsaamen, 1899a), and P. granifex (Kieffer, 1898). For each of these species, DNA sequences are provided, as well as detailed illustrations of the male terminalia and male flagellomeres. Four additional species are represented only with larva, female or incomplete specimens. The phylogeny of European Planetella is tentatively reconstructed based on the combined analysis of three gene markers (28S, 16S, COI), but without providing any new infrageneric classification. The phylogenetic placement of the genus Planetella within the subfamily Cecidomyiinae is reconstructed based on four gene markers (18S, 28S, 16S, COI). The monophyly of Planetella is well supported, as well as its placement in the supertribe Cecidomyiidi. The genera Acodiplosis Kieffer, 1895 and Putoniella Kieffer, 1896 appear as the closest relatives of Planetella. The delimitation of the tribe Hormomyiini is discussed.