Digger was a popular term used to describe Australian and New Zealand soldiers during the First World War. Diggers were seen to possess the characteristics of hardiness, democratic spirit, mateship and resourcefulness. The term is still used today as slang for an Australian soldier.

There are numerous theories about the origin of the term but it was not in wide use amongst soldiers until 1917. It was first applied to New Zealand troops before being adopted by the Australians as well. The term had been in wide use prior to the war on the Australian gold fields and New Zealand Kauri gum fields. Digger Dialects (W.H. Downing, 1919, ISBN 0195532333), a glossary of words and phrases used by Australian personnel during the First World War, says that "Digger" was first used in 1916.

Misguided sources claim the term originated from General Sir Ian Hamilton's message to the commander of the Australian and New Zealand Army Corps (ANZAC), General William Birdwood, on the evening of 25 April 1915, following the landing at Anzac Cove, which contained the postscript:

"P.S.—You have got through the difficult business, now you have only to dig, dig, dig, until you are safe."

While New Zealanders would call each other "Digger", all other nationalities, including Australians, tended to call them "Kiwis". The equivalent slang for a British soldier was "Tommy" from Tommy Atkins. However, while the Anzacs would happily refer to themselves as "Diggers", the British soldier generally resented being called "Tommy".

In 2001 Athletics Australia proposed to use "Diggers" as the nickname for the Australian athletics team but after a public outcry and protest from the RSL the proposal was withdrawn.