The parasitoid wasp genus Trichacis Förster is revised for Europe. Examination of historical and modern collections combined with DNA barcoding revealed the presence of only a single species in Europe, Trichacis tristis (Nees, 1834), redescribed here. Fourteen new synonymies are proposed for T. tristis: T. abdominalis Thomson, 1859 syn.nov.; T. bidentiscutum Szabó, 1981 syn.nov.; T. didas (Walker, 1835) syn.nov.; T. fusciala Szabó, 1981 syn.nov.; T. hajduica Szabó, 1981 syn.nov.; T. illusor Kieffer, 1916 syn.nov.; T. nosferatus Buhl, 1997 syn.nov.; T. pisis (Walker, 1835) syn.nov.; T. persicus Asadi & Buhl, 2021 syn.nov.; T. pulchricornis Szelényi, 1953 syn.nov.; T. quadriclava Szabó, 1981 syn.nov.; T. remulus (Walker, 1835) syn.nov.; T. vitreus Buhl, 1997 syn.nov.; T. weiperti Buhl, 2019 syn.nov.. Four species are transferred to Amblyaspis Förster: A. afurcata (Szabó, 1977) comb. nov., A. hungarica (Szabó, 1977), comb. nov., A. pannonica (Szabó, 1977) comb. nov., and A. tatika (Szabó, 1977) comb. nov. Intraspecific variation, biological associations, and taxonomic history are discussed. DNA barcodes are provided and analyzed in the context of worldwide Trichacis and its sister genus Isocybus Förster.