The Republic of South Africa is a constitutional democracy with three-tier system of government and an independent judiciary, operating in a parliamentary system. Legislative authority is held by the Parliament of South Africa. Executive authority is vested in the President of South Africa who is head of state and head of government, and his Cabinet. The President is elected from the Parliament to serve a fixed term. South Africa's government differs greatly from those of other Commonwealth nations. The national, provincial and local levels of government all have legislative and executive authority in their own spheres, and are defined in the South African Constitution as "distinctive, interdependent and interrelated".