The flag of Australia, also known as the Australian Blue Ensign, is based on the British Blue Ensign—a blue field with the Union Jack in the upper hoist quarter—augmented with a large white seven-pointed star (the Commonwealth Star) and a representation of the Southern Cross constellation, made up of five white stars (one small five-pointed star and four, larger, seven-pointed stars). Australia also has a number of other official flags representing its people and core functions of government.

Its original design (with a six-pointed Commonwealth Star) was chosen in 1901 from entries in a competition held following Federation, and was first flown in Melbourne on 3 September 1901, the date proclaimed in 1996 as Australian National Flag Day. A slightly different design was approved by King Edward VII in 1903. The current seven-pointed Commonwealth Star version was introduced by a proclamation dated 8 December 1908. The dimensions were formally gazetted in 1934, and in 1954 the flag became recognised by, and legally defined in, the Flags Act 1953 as the Australian National Flag.