Currently there are a number of nationalities who can travel to New Zealand without a visa for periods of up to 90 days (including the United States, all European Union member states, Canada, Brazil, Argentina, and Japan). Citizens from the UK can enter for up to six months visa free and Australians can stay in New Zealand indefinitely.
However, from July 2019 citizens of the 60 visa exempt countries for New Zealand will be able to pre-register an eTA visa waiver online before traveling to the country. This will become obligatory from October 1st, 2019.
The only exception will be citizens of Australia, who will continue to be able to travel to New Zealand visa-free. However, Australia permanent residents will also be required to apply for the eTA New Zealand (but not to pay the associated tourist levy).