The federation of Australia was the process by which the six separate British colonies of New South Wales, Queensland, South Australia, Tasmania, Victoria and Western Australia formed a federation. By force of the Constitution of Australia, on 1 January 1901 the Australian colonies collectively became the Commonwealth of Australia. The former colonies became component states of the Commonwealth.

Early efforts to bring about federation in the 1850s and 1860s were dogged by the lack of popular support for the movement. A number of conventions were held during the 1890s to develop a constitution for the Commonwealth. Sir Henry Parkes, Premier of New South Wales, was instrumental in this process. Fiji and New Zealand were originally part of this process, but decided not to join the federation.

Sir Edmund Barton was the caretaker Prime Minister of Australia at the inaugural 1901 federal election at which he retained the Prime Ministership.