Ansett Australia, originally Ansett Airways, was a major Australian airline group based in Melbourne, Victoria. The company operated domestically within Australia, and from the 1990s, to destinations in Asia. Following 65 years of operation, the airline went into administration in 2001 following a financial collapse and subsequent liquidation in 2002, subject to a deed of company arrangement. Ansett's last flight touched down on 5 March 2002.

The company was founded by Reginald "Reg" Ansett in 1935 as Ansett Airways Pty Ltd. This was an offshoot of his road transport business, which had become so successful it was threatening the freight and passenger revenue of Victorian Railways. This led the state government to legislate to put private road transport operators out of business. Reg Ansett countered by establishing an airline, as aviation was under control of the federal government and beyond the reach of the state government.

Ansett's first route between Hamilton and Melbourne operated by a Fokker Universal monoplane commenced on 17 February 1936. The rapid success of the airline led Ansett to float the business in 1937. As the route network expanded, Ansett Airways imported Lockheed Electra aircraft. During World War II, Ansett opted to suspend all scheduled services, except the Hamilton service, in favour of more lucrative work for the United States Army Air Forces. After the war, Ansett battled to re-establish his domestic routes using war-surplus Douglas DC-3s, converted from C-47s and the remaining Lockheed Electras.

At this time, the Australian domestic airline travel sector was dominated by Australian National Airways (ANA), established in 1936 by a consortium of British-financed Australian shipowners. The Chifley federal government was determined to establish a state-owned airline to operate all domestic and international services. It was eventually thwarted in this aim by the High Court of Australia, so it established Trans-Australia Airlines (TAA) to operate in competition with ANA.

Ansett Airways remained a big player as ANA and TAA battled for supremacy in the 1940s and 1950s. Ansett operated around the big two, maintaining budget-fare interstate operations with DC-3s and later Convair CV-340s previously operated by Braniff International Airways in the United States. The airline was backed up by extensive road transport operations, including Ansett Freight Express and Ansett Pioneer Coaches, as well as the Ansair coach-building operation.

The Menzies government, while supporting TAA, because of the excellent dividends it paid to the government, wanted to avoid TAA having a monopoly on domestic services if ANA collapsed, as seemed likely. The only alternative, as it transpired, was for Ansett to buy the ANA operation. Ansett's bid had a number of financial supporters, most prominent of these being the Shell Oil Company. Douglas Aircraft Company was also concerned about ANA's demise, as TAA had ceased to be a customer for their aircraft. The ANA directors fiercely resisted this initially, but in October 1957, succumbed to Ansett's offer of £3.3 million for their airline. The new entity was called Ansett-ANA, the name it retained until 1 November 1968, when it became Ansett Airlines of Australia.

Ansett-ANA's excellent profit record was, at least in part, courtesy of the Menzies government's Two Airlines Policy that limited competition. The policy effectively blocked any other domestic interstate operators by way of a ban on importation of aircraft without a government licence. From 1957 until the 1980s, under the strict rules set down by the Two Airlines Policy, Ansett and TAA operated as virtual carbon copies of each other, operating the same aircraft at the same times, to the same destinations, at fares, which were identical (under strict federal government policy). If either airline wished to change its fares, they had to obtain federal government approval.

Reg Ansett then set out to ensure no other competitors could rise up to challenge his airline. He took control of Adelaide-based Guinea Airways (renamed Airlines of South Australia) and Sydney-based Butler Air Transport (renamed Airlines of New South Wales). The takeover of Butler was achieved with covert support from the Menzies government and by Ansett engineering his employees' purchases of Butler shares (in a similar way as had just been attempted by Butler). He then flew the employees to a general meeting in Sydney and forced a vote in favour of selling out to Ansett. Ansett later purchased Perth-based MacRobertson Miller Airlines, buying 70% of the shares in 1963 and completing the takeover in November 1968. Unlike Ansett's other regional acquisitions MMA retained its own identity (aircraft flew in Ansett livery but with MMA logotypes) for many years, finally becoming Airlines of Western Australia in 1981.