The current boundaries of New Zealand are set out in the Letters Patent Constituting the Office of Governor-General of New Zealand 1983.

The Realm of New Zealand comprises New Zealand, Tokelau, the Ross Dependency and the self-governing states of the Cook Islands and Niue. A succinct summary of New Zealand's imperial aspirations in the Pacific, and its acquisitions of territories, can be found here: https://teara.govt.nz/en/pacific-islands-and-new-zealand

The boundaries of New Zealand changed somewhat between 1840 and 1887. The subantarctic islands were added to New Zealand by the Letters Patent 1842. The New Zealand Constitution Act 1846 excluded the Auckland and Campbell islands - probably by by accident - but the New Zealand Boundaries Act 1863 corrected the error.

The Kermadec islands were added to the Colony in 1887.

The Ross Dependency (the parts of Antarctica between 160° east and 150° west longitude, andthe islands lying between those degrees of longitude and south of latitude 60° south) was claimed by the United Kingdom in 1923, and was handed over to New Zealand to administer.