The constitution of New Zealand is the sum of laws and principles that determine the political governance of New Zealand. Unlike many other nations, New Zealand has no single constitutional document. It is an uncodified constitution, sometimes referred to as an "unwritten constitution", although the New Zealand constitution is in fact an amalgamation of written and unwritten sources. The Constitution Act 1986 has a central role, alongside a collection of other statutes, orders in Council, letters patent, decisions of the courts, principles of the Treaty of Waitangi, and unwritten traditions and conventions. There is no technical difference between ordinary statutes and law considered "constitutional law"; no law is accorded higher status. In most cases the New Zealand Parliament can perform "constitutional reform" simply by passing acts of Parliament, and thus has the power to change or abolish elements of the constitution. There are some exceptions to this though – the Electoral Act 1993 requires certain provisions can only be amended following a referendum.
After decades of self-governance, New Zealand gained full statutory independence from Britain in 1947. It is a constitutional monarchy with a parliamentary democracy. The monarch of New Zealand is the head of state – represented in the Realm of New Zealand by the governor-general – and is the source of executive, judicial and legislative power, although effective power is in the hands of ministers drawn from the democratically elected New Zealand House of Representatives. This system is based on the "Westminster model", although that term is increasingly inapt given constitutional developments particular to New Zealand. For instance, New Zealand introduced a unicameral system within a decade of its statutory independence.