The flag of New Zealand (Māori: Te haki o Aotearoa), also known as the New Zealand Ensign, is based on the British maritime Blue Ensign – a blue field with the Union Jack in the canton or upper hoist corner – augmented or defaced with four red stars centred within four white stars, representing the Southern Cross constellation.

New Zealand's first national flag, the flag of the United Tribes of New Zealand, was adopted in 1834, six years before New Zealand's separation from New South Wales and creation as a separate colony following the signing of the Treaty of Waitangi in 1840. Chosen by an assembly of Māori chiefs at Waitangi in 1834, the flag was of a St George's Cross with another cross in the canton containing four stars on a blue field. After the formation of the colony in 1840, British ensigns began to be used. The current flag was designed and adopted for use on the colony's ships in 1869, was quickly adopted as New Zealand's national flag, and given statutory recognition in 1902.

For several decades there has been debate about changing the flag. In 2016, a two-stage binding referendum on a flag change took place with voting on the second final stage closing on 24 March. In this referendum, the country voted to keep the existing flag by 57% to 43%.

The flag should be rectangular in shape and its length should be two times its width, translating into an aspect ratio of 1:2. It has a royal blue background with a Union Jack in the canton, and four five-pointed red stars centred within four five-pointed white stars on the fly (outer or right-hand side).

According to the Ministry for Culture and Heritage, the government department responsible for the flag, the royal blue background is "reminiscent of the blue sea and sky surrounding us", and the stars "signify [New Zealand's] place in the South Pacific Ocean". The New Zealand Government history website states: "Its royal blue background is derived from the ensign of the Blue Squadron of the Royal Navy."