Abstract Drilling for thermal water for domestic purposes commenced in Rotorua in the 1930s and rapidly developed on a commercial scale in the 1940s, when it was discovered that steam could be obtained by drilling deeper. Exploration for steam to generate electric power commenced at Wairakei in 1950 during a period of power shortage. Since then, the use of geothermal energy has been developed at Wairakei and Kawerau, and investigations have been extended into other fields. The initial aim at Wairakei was to obtain steam at high pressure, but drilling soon showed that the young volcanic strata beneath the field are saturated with water in which the temperature increases downward in accord with the boiling point for the increasing pressure, to a limiting value of about 260°C. Steam flashes from the hot water rising in the wells as the pressure falls, and is separated at selected pressures at the surface and put through turbines. At Wairakei the sole product is electric power; however, at Kawerau the steam is used for process purposes in the Tasman Pulp and Paper Company mill, and only surplus steam is used for the generation of electric power up to a maximum capacity of 10 Mw. Other fields prospected by drilling are Waiotapu, Reporoa, Te Kopia, Orakeikorako, Tauhara, Rotokawa, and Ngawha. With the exception of Ngawha, which is located in the Northland area, all the fields lie within the Taupo volcanic zone in the central North Island (see Healy, this volume, Fig. 2).