The geographical configuration and hydrological character of the sub-tropical convergence, the boundary between waters of sub-tropical and sub-antarctic origin, in the vicinity of New Zealand are discussed. As a background to this discussion some data are given on the seasonal variation of surface temperature in New Zealand coastal waters. The convergence follows approximately the isotherms of 15° C in February and 10° C in August and the isohalines of 34.7 to 34.8‰ with little seasonal variation. It is characterized at the surface by steep horizontal gradients of temperature and salinity. Off the west coast of New Zealand surface water seems to be predominantly sub-tropical in character, in Foveaux Strait and off South Island being probably derived from the East Australian Current, with the northern area probably subject at times to direct entry of sub-tropical water from the north-east of New Zealand. Wind-induced upwelling may often result in lowered temperatures close to the west coast of North Island, and pronounced drops in surface temperature are consistently found between the Three Kings Islands and the mainland, and off Cape Farewell. South of New Zealand sub-tropical influence is felt in sufficient degree to raise significantly the temperature and salinity of surface waters over the Campbell Plateau. East of South Island, sub-antractic water lies off the Otago coast and extends northwards along the east coast in a narrow band as far as the Castle Point region, North Island, where the sub-tropical convergence tends to meet the coast. From this point the convergence is well defined and trends sharply southwards under the action of the East Cape Current, tongues of sub-tropical water tending to come close inshore in southern Cook Strait and off Kaikoura. Offshore from the Banks Peninsula area the convergence trends eastwards towards the Chatham Islands and probably becomes less well defined at the surface. An area of probable upwelling is noted to occur frequently between East Cape and the Ranfurly Bank.