This monograph incorporates a systematic revision of the freshwater mussels of the Australian Region (Australia, New Zealand, New Guinea and the Solomon Islands). Previous systematic works are revised and discussed. Details of the taxonomic procedures used in the present work are presented. One aberrant New Guinea genus, Haasodonta, with two species is referred provisionally to the family Unionidae Fleming, subfamily Rectidentinae Modell. The remainder of the Australasian species are assigned to the family Mutelidae Gray. Four subfamilies, Velesunioninae Iredale, Lortiellinae Iredale, Hyridellinae Iredale, and Cucumerunioninae Iredale, are recognized. These include eight genera, Velesunio Iredale, Alathyria Iredale, Weatralunio Iredale, Microdontia Tapparone Canefri, Lortiella Iredale, Hyridella Swainson, Cucumerunio Iredale, and Virgus Simpson. The genus Hyridella includes four subgenera, Hyridella s.s., Protohyridella Cotton & Gabriel, Nesonaia Haas, and a new subgenus for H. menziesi Gray. These eight genera include 27 species, three of which are polytypic. Three additional species are considered of doubtful validity and two nominal species are listed as nomina dubia. Each taxon is redescribed and all available data of shell morphology, soft anatomy, larval stages, distribution, and type material are presented. The distribution of the Australian and New Guinea species in relation to the fluvifaunal provinces of Iredale and Whitley is considered and a new name is proposed for the fluvifaunula of southern New Guinea. The evolutionary relationships of the Australasian freshwater mussels are discussed and it is suggested that, with one exception, they arose from a single ancestral stock and have subsequently differentiated into four subfamilies within this region. This view is supported by the close anatomical similarity between them.