Holders of US passports do NOT need a visa to just go on vacation to New Zealand if you plan to stay 90 days or less. Also, your passport must not expire for at least 90 days beyond the date you depart from New Zealand. If you want to stay longer, you need to check specific information because you will need a visa. If you hold a passport issued by a country other than the US, you'll need to check specific information.
New Zealand Working Holiday visa
Soak up the true culture of New Zealand by working there! Americans can apply for a Working Holiday Visa, which allows you stay for up to 12 months working and traveling around the country. You will usually get a response within a few days of applying asking for more information or letting you know the decision. Once approved, you have 12 months to arrive in New Zealand and can work for up to 12 months once you get there.