A revised diagnosis and taxonomic notes on the Holarctic fairyfly Polynema (Doriclytus) atratumHaliday, 1833 (Hymenoptera: Mymaridae), a common species in northern Europe, are given. Polynema ruficolleKieffer, 1913, syn. nov. (Scotland, United Kingdom), P. micropteraBakkendorf, 1934, syn. nov. (Denmark, for which a lectotype is designated), as well as P. fennicumSoyka, 1946, syn. nov. (Finland, originally described as P. fennica), P. novickyiSoyka, 1946, syn. nov. (Austria), P. aequicoloratum (Soyka, 1950), syn. nov. (Finland, originally described as Novickyella aequicolorata), P. auripedicellatum (Soyka, 1950), syn. nov. (Finland, originally described as Novickyella auripedicellata), P. calceatiscapus (Soyka, 1950), syn. nov. (Finland, originally described as Novickiella [sic] calceatiscapus), P. fennicosimile (Soyka, 1950), syn. nov. (Finland, originally described as Novickyella fennicosimilis), P. palustre (Soyka, 1950), syn. nov. (Austria, originally described as Novickyella palustrisSoyka, 1950, for which a lectotype is designated), P. arcticumSoyka, 1956, syn. nov. (Finland, originally described as P. arctica), P. brevicorneSoyka, 1956, syn. nov. (?Italy, originally described as P. brevicornis), P. globosiventreSoyka, 1956, syn. nov. (Poland, originally described as P. globosiventris), P. palustreSoyka, 1956, syn. nov. (Austria, originally described as P. palustris), and P. soykaiÖzdikmen, 2011, syn. nov. (unnecessary replacement name for P. palustre Soyka, 1956 nec P. palustre (Soyka, 1950)) are all synonymized under P. (Doriclytus) atratum. Primary types of the new synonyms, for which label data are provided, are illustrated with digital images. Females of P. (Doriclytus) atratum are usually fully winged but occasionally brachypterous, while males are always macropterous. Polynema (Doriclytus) atratum is for the first time recorded outside Europe, from the Asian part of the Palaearctic Region (Armenia) and the Nearctic Region (British Columbia, Canada). Numerous other records of this species, particularly from Finland and the adjacent countries, are given.