The Constitution of Australia is the law under which the Australian Commonwealth government operates. It consists of several documents. The most important is the Constitution of the Commonwealth of Australia. The Constitution was approved in referendums held over 1898 - 1900 by the people of the Australian colonies, and the approved draft was enacted as a section of the Commonwealth of Australia Constitution Act 1900 (Imp), an Act of the Parliament of the United Kingdom. The Constitution came into force on 1 January 1901. Even though the Constitution was originally given legal force by an Act of the United Kingdom parliament, as Australia is now an independent country, the United Kingdom parliament has no power to change the Constitution, and only the Australian people can amend it (by referendum). Letters patent issued by the Crown, on the advice of Australian ministers, are also part of the Constitution of Australia.

Other pieces of legislation have constitutional significance for Australia. These are the Statute of Westminster, as adopted by the Commonwealth in the Statute of Westminster Adoption Act 1942, and the Australia Act 1986, which was passed in equivalent forms by the Parliaments of every Australian state, the United Kingdom, and the Australian Federal Parliament. Together, these Acts had the effect of severing all constitutional links between Australia and the United Kingdom. Even though the same person, Queen Elizabeth II, is the head of state of both countries, she acts in a distinct capacity as head of state of each.

Under Australia's common law system, the High Court of Australia and the Federal Court of Australia have the authority to interpret constitutional provisions. Their decisions determine the interpretation and application of the constitution.