Australian football, also called Australian rules football or Aussie rules, or more simply football or footy, is a contact sport played between two teams of 18 players on an oval field, often a modified cricket ground. Points are scored by kicking the ovoid ball between the central goal posts (worth six points), or between a central and outer post (worth one point, otherwise known as a "behind").

During general play, players may position themselves anywhere on the field and use any part of their bodies to move the ball. The primary methods are kicking, handballing and running with the ball. There are rules on how the ball can be handled; for example, players running with the ball must intermittently bounce or touch it on the ground. Throwing the ball is not allowed, and players must not get caught holding the ball. A distinctive feature of the game is the mark, where players anywhere on the field who catch the ball from a kick (with specific conditions) are awarded unimpeded possession. Possession of the ball is in dispute at all times except when a free kick or mark is paid. Players can tackle using their hands or use their whole body to obstruct opponents. Dangerous physical contact (such as pushing an opponent in the back), interference when marking, and deliberately slowing the play are discouraged with free kicks, distance penalties, or suspension for a certain number of matches depending on the severity of the infringement. The game features frequent physical contests, spectacular marking, fast movement of both players and the ball, and high scoring.

The sport's origins can be traced to football matches played in Melbourne, Victoria, in 1858, inspired by English public school football games. Seeking to develop a game more suited to adults and Australian conditions, the Melbourne Football Club published the first laws of Australian football in May 1859.

Australian football has the highest spectator attendance of all sports in Australia while the Australian Football League (AFL), the sport's only fully professional competition, is the nation's wealthiest sporting body. The AFL Grand Final, held annually at the 100,000-capacity Melbourne Cricket Ground, is the highest-attended club championship event of any football code. The sport is also played at amateur level in many countries and in several variations. Its rules are governed by the AFL Commission with the advice of the AFL's Laws of the Game Committee.

Australian football is known by several nicknames, including Australian rules football, Aussie rules, football and footy. In some regions, where other codes of football are more popular, the sport is most often called AFL after the Australian Football League, while the league itself also uses this name for local competitions in some areas.

Primitive forms of football were played sporadically in the Australian colonies in the first half of the 19th century. Compared to cricket and horse racing, football was considered a mere "amusement" by colonists at the time, and while little is known about these early one-off games, evidence does not support a causal link with Australian football. In Melbourne, in 1858, in a move that would help to shape Australian football in its formative years, private schools (then termed "public schools" in accordance with nomenclature in England) began organising football games inspired by precedents at English public schools. The earliest match, held on 15 June, was between Melbourne Grammar and St Kilda Grammar. Football teams sprang up from cricket clubs in 1858 and began mostly playing inter club 'scratch matches."

On 10 July 1858, the Melbourne-based Bell's Life in Victoria and Sporting Chronicle published a letter by Tom Wills, captain of the Victoria cricket team, calling for the formation of a "foot-ball club" with a "code of laws" to keep cricketers fit during winter. Born in Australia, Wills played a nascent form of rugby football while a pupil at Rugby School in England, and returned to his homeland a star athlete and cricketer. Two weeks later, Wills' friend, cricketer Jerry Bryant, posted an advertisement for a scratch match at the Richmond Paddock adjoining the Melbourne Cricket Ground (MCG). This was the first of several "kickabouts" held that year involving members of the Melbourne Cricket Club, including Wills, Bryant, W. J. Hammersley and J. B. Thompson. Trees were used as goalposts and play typically lasted an entire afternoon. Without an agreed-upon code of laws, some players were guided by rules they had learned in the British Isles, "others by no rules at all". Another milestone in 1858 was a 40-a-side match played under experimental rules between Melbourne Grammar and Scotch College, held at the Richmond Paddock. Umpired by Wills and teacher John Macadam, it began on 7 August and continued over two subsequent Saturdays, ending in a draw with each side kicking one goal. It is commemorated with a statue outside the MCG, and the two schools have since competed annually in the Cordner–Eggleston Cup, the world's oldest continuous football competition.

Since the 1920s, it has been suggested that Australian football may have been derived from the Irish sport of Gaelic football. Only recently has archival evidence been uncovered in favour of the Irish influence on the Australian rules game, showing before the GAA code was established, during the pre-GAA football era in East Munster, Templemore Citizen-Garrison rules was played since 1847 in Templemore, and from 1858 seeded in Graham's Paddock, Hotham Hill, North Melbourne. Thus, through migration helped the two codes evolve in a similar direction. Another theory, first proposed in 1983, posits that Wills, having grown up among Aboriginals in Victoria, may have seen or played the Aboriginal ball game of Marn Grook, and incorporated some of its features into early Australian football. There is only circumstantial evidence that he knew of the game, and according to biographer Greg de Moore's research, Wills was "almost solely influenced by his experience at Rugby School".