Fifteen species of Plinthisus are reported from Australia, all of them previously undescribed. The new species are: P. woodwardi, P. australiensis, P. tasmaniensis, P. kangarooensis, P. acrocephalus, P. nudus, P. sericeus, P. platycephalus, P. mullewa, P. dampieris, P. reticulatus, P. tindalís, P. flíndersi, P. bassianus and P. grossi. P. woodwardi is also reported from New Zealand. The species are segregated into five groups. Their distributions within Australia and relationships to Oriental, African and South American taxa are discussed. A key to species is included. Plinthisus tineoides (Distant), an Oriental species, is redescribed and Locutius atratus Distant, 1918 and Locutius pallescens Distant, 1918 placed as junior synonyms. The ecological habitats and host plant relationships of P. australiensis, P. nudus, P. bassianus and P. grossi are discussed. Descriptions of nymphs are given for P. woodwardi, P. australiensis and P. grossi. Sixty figures are included illustrating dorsal views, spermatheca, metathoracic scent gland areas, eggs, wings, aedeagus, sperm reservoirs, parameres and abdominal details.