ESTA is not a visa. This is an important distinction. A valid travel authorization (ESTA) does not meet the legal requirements of visa. Travellers that possess a valid visa for the United States may travel to the U.S. with that visa for the purpose it was issued. Travellers traveling on valid visa do not need to apply for an additional ESTA. In the same way that a valid visa does not guarantee admission to the United States, an approved ESTA is not a guarantee of admission either.
After January 12, 2009, all New Zealand Citizens entering the United States under the Visa Waiver Program are required to apply for ESTA (Electronic System for Travel Authorization). ESTA is a required "travel permit;" it is not an actual U.S. visa. The ESTA requirement applies to travellers entering the United States by air or sea under the Visa Waiver Program. ESTA Applicants must also have a valid machine-readable passport. New Zealand travellers without an approved ESTA Travel Authorization or a valid U.S. Visitor Visa will be denied boarding on all U.S.-bound flights. The U.S. government recommends to apply for ESTA as early as possible. New Zealand travellers should apply for ESTA at least 72 hours prior to traveling to the United States.
Citizens of all the Visa Waiver Countries may travel to the United States without a visa. There are certain restrictions in the Visa Waiver Program, but there is still the main advantage, that no visa is required. If you are a New Zealand citizen holding a New Zealand Passport you can apply for ESTA (Travel Authorization) online through the Electronic System for Travel Authorization - also called “ESTA”. This program enables visits to the United States for up to 90 days for tourism, business, transit, or medical reasons without the need to apply for a USA visa.
The following countries are currently partaking in the Visa Waiver Program: Andorra, Australia, Austria, Belgium, Brunei, Chile, Czech Republic, Chile, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Republic of Malta, Monaco, the Netherlands, New Zealand, Norway, Portugal, San Marino, Singapore, Slovakia, Slovenia, South Korea, Spain, Sweden, Switzerland, Taiwan and the United Kingdom.