The Federation of Australia was the process by which the six separate British self-governing colonies of Queensland, New South Wales, Victoria, Tasmania, South Australia, and Western Australia agreed to unite and form the Commonwealth of Australia, establishing a system of federalism in Australia. The colonies of Fiji and New Zealand were originally part of this process, but they decided not to join the federation. Following federation, the six colonies that united to form the Commonwealth of Australia as states kept the systems of government that they had developed as separate colonies, but they also agreed to have a federal government that was responsible for matters concerning the whole nation. When the Constitution of Australia came into force, on 1 January 1901, the colonies collectively became states of the Commonwealth of Australia.

The Constitution of Australia is the fundamental law that governs the political structure of Australia. It is a written constitution, that establishes the country as a federation under a constitutional monarchy governed with a parliamentary system. Its eight chapters sets down the structure and powers of the three constituent parts of the federal level of government: the Parliament, the executive government and the judicature.