New Zealand's possession of the fourth-largest exclusive economic zone in the world, and rights to the seabed resources of the continental shelf of which it is part, results from the United Nations Convention on the Law of the Sea (UNCLOS). Adopted in 1982 after nearly 10 years of negotiation, UNCLOS is one of the great multilateral achievements of the 20th century. In addition to setting up the exclusive economic zone system, UNCLOS guarantees the free passage of shipping through international straits and territorial seas, and navigational freedom on the open sea. The convention is widely adhered to, including by states who have not signed it.

The map above shows New Zealand's exclusive economic zone (the central highlighted area) and its continental shelf zone (the outer highlighted area), whose boundary was agreed with Australia. In 2011 the upper right hand section of the boundary had not yet been settled with Tonga and Fiji.