The formation of the Government of Western Australia is prescribed in its Constitution, which dates from 1890, although it has been amended many times since then. Since 1901 Western Australia has been a state of the Commonwealth of Australia, and the Australian Constitution regulates its relationship with the Commonwealth.
Under the Australian Constitution, Western Australia ceded certain legislative and judicial powers to the Commonwealth, but retained complete independence in all other areas.
Western Australia is governed according to the principles of the Westminster system, a form of parliamentary government based on the model of the United Kingdom.
Legislative power rests with the Parliament of Western Australia, which consists of the Crown, represented by the Governor of Western Australia, and the two Houses, the Western Australian Legislative Council and the Western Australian Legislative Assembly.
Executive power rests formally with the Executive Council, which consists of the Governor and senior ministers. In practice executive power is exercised by the Premier of Western Australia and the Cabinet, who are appointed by the Governor, but who hold office by virtue of their ability to command the support of a majority of members of the Legislative Assembly.
Judicial power is exercised by the Supreme Court of Western Australia and a system of subordinate courts, but the High Court of Australia has final jurisdiction. Other federal courts also have jurisdiction over certain matters, but only insofar as the Australian Constitution grants the federal government power to make laws for such matters.