The species that comprise a morphostatic radiation in southeastern Australia of the hydrobiid genus Austropyrgus Cotton are described using shell, opercular, anatomical and radular characters, and the genus is redefined. The previously described taxa have been included under several generic names, including Fluvidona (now a separate genus), Rivisessor, Pupiphryx and Angrobia, which are now treated as synonyms of Austropyrgus. Seventy-four species are described from southeastern Australia, fifty-seven of them new. These are grouped into six informal morphological groups to aid identification. Two recently described outlying species, A. bunyaensis from Mt Bunya, southern Queensland and A. centralia from Dalhousie Springs, northern South Australia, are not included in this revision. Members of the genus are typically found in streams, although a few species live in springs, rivers or lakes. A large number of the species have restricted distributions and several are known only from single locations. In southern New South Wales, Victoria and South Australia Austropyrgus is the dominant native freshwater hydrobiid genus whereas in Tasmania it is often sympatric with the native freshwater hydrobiid genera Beddomeia and/or Phrantela.