Polyblastia s.str. (Verrucariaceae, Chaetothyriomycetidae) of Northern Europe and the adjacent Arctic is revised. The morphology and the history of the exploration of Polyblastia s.str. is described. Twenty-five species are recognized, twelve of them being new. A molecular phylogeny of the genus based on the internal transcribed spacers (ITS) of nuclear ribosomal DNA is presented and compared with earlier suggestions on infrageneric classification. Polyblastia s.str. is compared with related and similar genera, and the traditional delimitation of genera inthe Verrucariaceae is discussed. A key to the species is given and the morphology, ecology and distribution of the species are described along with notes on synonymy and nomenclature. Lectotypes of 13 taxa have been designated and comments on additional species frequently referredto Polyblastia in 20:th century lichenological literature from the area have been included. ITS, Key, molecular phylogeny, nomenclature, Polyblastia, revision, Verrucariaceae, taxonomy. New taxa: Polyblastia aurorae S. Savić & Tibell sp. nov., P. baltica S. Savić & Tibell sp. nov., P. borealis S. Savić & Tibell sp. nov., P. cataractae S. Savić & Tibell sp. nov., P. dimidiata S. Savić & Tibell sp. nov., P. fusca S. Savić & Tibell sp. nov., P. inconspicua S. Savić & Tibell sp. nov., P. media S. Savić & Tibell sp. nov., P. neglecta S. Savić & Tibell sp. nov., P. nordinii S. Savić & Tibell sp. nov., P. potamophila S. Savić & Tibell sp. nov., P. pulchra S. Savić & Tibell sp. nov.