Big Brother Australia (also known simply as Big Brother) is an Australian reality show based on the international Big Brother format created by John de Mol Jr..

Following the premise of other versions of the format, the show features a group of contestants, known as "housemates" who live together in a specially constructed house that is isolated from the outside world. The housemates are continuously monitored during their stay in the house by live television cameras as well as personal audio microphones. Throughout the course of the competition, housemates are evicted from the house – eliminated from the competition. The last remaining housemate wins the competition and is awarded a cash prize.

Big Brother was produced from 2001 and ran for eight seasons and a Celebrity edition on Network Ten before the network cancelled it in July 2008 after experiencing audience erosion and controversy. Big Brother returned in 2012 on the Nine Network. Nine's iteration of the series lasted 3 seasons and was not renewed beyond 2015. Each of the first eleven previous seasons were produced by Endemol Australia and Endemol Southern Star.

In 2019, the Seven Network picked up the series, which was produced by Endemol Shine Australia. The series ran for four regular seasons (including a special edition featuring new and returning Housemates in commemoration of the show's 21st anniversary in 2022) as well a new celebrity edition titled Big Brother VIP. As a result of a poor reception to the 15th season, a planned 16th season (and the fifth to be aired by Seven) that was announced for 2024 did not eventuate.

On 16 September 2024, it was confirmed that Big Brother would be returning to Network 10 for its sixteenth season in 2025, with live nominations, live evictions, and a 24/7 livestream returning.