Postia was circumscribed by mycologist Elias Magnus Fries in his 1874 work Hymenomycetes europaei.[2] The genus name honours Swedish naturalist Hampus von Post (1822–1911).[3]
A 2008 estimate placed 30 species in the genus.[4] As of June 2018[update], Index Fungorum accepts 57 species of Postia:[5]
In a 2018 revision of the Postia caesia complex, Otto Miettinen and colleagues proposed four new combinations, and described ten new species:[19]