New Zealand follows a dualist approach to the domestic effect of international treaties. This is similar in approach to other Commonwealth countries such as the United Kingdom, Canada and Australia. The dualist system means that in order for the treaty obligations to be given the force of law domestically, they cannot simply be ratified - they must be incorporated into domestic legislation.
In general, New Zealand courts apply a rule of statutory interpretation whereby domestic statutes are read, so far as their wording allows, consistently with international obligations (New Zealand Air Line Pilots’ Association Inc v Attorney-General  3 NZLR 269, 289) because there is a presumption that Parliament does not intend to enact legislation that is inconsistent with New Zealand's unincorporated international obligations. For more on this topic, see eg: Alice Osman, 'Demanding Attention: the Roles of Unincorporated International Instruments on Judicial Reasoning' (2014) 122 New Zealand Journal of Public and International Law 345-377. An unpublished version of this article is freely available online. See also Margaret Wilson, Judy McGregor and Sylvia Bell, ‘The Impact of Economic and Social Human Rights in New Zealand Case Law’ (2015) 21(1) Australian Journal of Human Rights 143-165, in which the authors argue, with specific reference to the International Covenant on Economic, Social and Cultural Rights, that courts are reluctant to grant remedies without this treaty being explicitly incorporated into the domestic law.
See also the NZ chapters in:
New Zealand Treaties Online contains the New Zealand Treaty Series (NZTS), the official record of New Zealand’s binding legal obligations at international law. The Ministry of Foreign Affairs and Trade is the New Zealand repository of all treaties. The Treaties Online website provides information about treaties that New Zealand is party to, as well as ‘treaties in progress’ which are currently under negotiation or awaiting ratification.
Most New Zealand multilateral and bilateral treaties are also part of the United Nations Treaty Series (UNTS) 1946 +, and its precursors, the League of Nations Treaty Series (LNTS) 1920-1944) and the Consolidated Treaty Series (ConTS) 1648-1919 (also known as Parry's Treaty Series, and available online on Oxford Historical Treaties).
See the Treaties page of our Public International Law Research Guide for more information about treaties and the UN Treaty Series.
For citation purposes, if a treaty is part of the UNTS (or any of its predecessors) and the NZTS, then the UNTS citation is to be preferred. See Chapter 7.4 (pp 125-127) of the Australian Guide to Legal Citation. For more information, see the Citing Treaties box on the Treaties page of our Public International Law Guide.
New Zealand is currently party to more than 1,600 treaties, as well as many others that are not yet in force.
The Ministry of Foreign Affairs and Trade (MFAT) conducts the Government's business with foreign governments and international organisations. MFAT's Legal Division oversees the process by which the Government enters into or withdraws from treaties.
See information about the New Zealand treaty-making process on the MFAT Treaty website.