The Australian Constitution came into force with the inauguration of the Commonwealth of Australia in January 1901. The Constitution was originally laid out in a UK act- the Commonwealth of Australia Constitution Act 1900 (63 & 64 Victoria c12). It has subsequently been amended.
The Commonwealth Constitution maps out the federal/regional distribution of power.
Other important constitutional legislation includes the Statute of Westminster Adoption Act 1942 (Australia established as an independent Commonwealth nation), and the Australia Act 1986 (completed the process of independence from the UK).
States and territories have their own constitutions.