New Zealand citizens do not need a visa if they are planning to visit the United States for the purposes of tourism, business, or transit for a duration of 90 days or less.
However, they are required to have an ESTA travel authorization, as stipulated in the Visa Waiver Program.
The ESTA allows travelers to stay within the United States for up to 90 days. It is valid for 2 years from the date of issue, or until the traveler’s passport expires (whichever happens first).
The ESTA is necessary for entry into the United States via a commercial flight or cruise.
The ESTA is a multiple-entry authorization, which means that visitors from New Zealand can travel in and out of the United States as many times as they would like within the allotted time period.
An approved ESTA application means that you can have multiple trips to the U.S. of a short duration for the purposes of business or tourism during the validity of ESTA. Keep in mind however that if you travel to the U.S. frequently and stay for long periods of time, CBP officers at the port of entry may question your intentions in the U.S. If your plans change and you decide that you wish to stay in the U.S. longer or if you wish to work or study, you will need to apply for a visa at the U.S. Consulate in New Zealand.