The cymonomid crabs of New Zealand and Australia are revised. Prior to the present study, three species each were known from New Zealand and Australia, respectively. Here, eight new species are described and the six previously known species are redescribed and refigured based on type material. Although based on few locality records, the New Zealand species of Cymonomus show north-south distributions corresponding to the Aupourian and Cookian Provinces, respectively, demarcated by the subtropical convergence in the vicinity of the Chatham Rise. Notably, the New Zealand species, C. clarki, is the southernmost occurring cymonomid worldwide. Most Australian records of Cymonomus are from southern waters; few are known from northern Western Australia or Queensland, and none from the Northern Territory, probably reflecting limited sampling effort. One new species from Tasmania is unique in Cymonomus in having transparent, well-defined corneas, rather than opaque-translucent corneal surfaces that are undifferentiated from surrounding cuticle. The New Zealand and Australian species of Cymonomus belong to species groups that range widely in the Indo-West Pacific, or even globally; whether these groups represent natural divisions awaits revision of the Atlanto-East Pacific cymonomid fauna. A key to the species of Cymonomus from New Zealand and Australia is provided.