New Zealand is governed under The Consitution Act of 1986, adopted in 1987, as well as other legal documents. The monarch of Great Britain and Northern Ireland, represented by the governor-general, is the head of state. The government is headed by the prime minister, who is appointed by the governor-general following legislative elections. Members of the 120-seat unicameral parliament (the House of Representatives) are elected by popular vote for three-year terms using a system of mixed constituency and proportional representation. Administratively, the country is divided into 16 regions and one territory (the Chatham Islands). New Zealand is a member of the Commonwealth of Nations.