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. Sources of the constitution The constitution includes, but is not limited to, the following sources: Elements The New Zealand constitution is uncodified and is to be found in formal legal documents, in decisions of the courts, and in practices (some of which are described as conventions). It establishes that New Zealand is a constitutional monarchy, that it has a parliamentary system of government, and that it is a representative democracy. It increasingly reflects the fact that the Treaty of Waitangi is regarded as a founding document of government in New Zealand. The constitution must also be seen in its international context because New Zealand governmental institutions must increasingly have regard to international obligations and standards. The Constitution Act 1986 describes the three branches of Government in New