The Big Day Out (BDO) is an annual music festival held in several cities in Australia and New Zealand in late January. It started in Sydney in 1992, spread to Adelaide, Melbourne and Perth by 1993, with the Gold Coast and Auckland joining in 1994. As of 2003, it has featured seven or eight stages (depending on the venue) accommodating popular contemporary rock music, electronic music, mainstream international acts and local acts. It is produced by Creative Festival Entertainment, an Australian based partnership between Ken West and C3 Presents.

The festival began in 1992 as a Sydney-only show with Violent Femmes as the headline act, along with Nirvana and a range of other foreign and local alternative music acts playing at the Hordern Pavilion. In the months preceding the event, Nirvana's Nevermind was released and became an international smash hit, therefore guaranteeing the success of the festival. In 1993, the festival was extended to include Melbourne, Perth, and Adelaide.

Since 1994, the Big Day Out has travelled annually to Auckland, the Gold Coast, Sydney, Adelaide, Melbourne and Perth during a three-week period. The tour through the southern-hemisphere summer has become "the festival overseas acts want to be on". In 1997, organisers Ken West and Vivian Lees announced they were taking a year off, causing concern that the festival was coming to an end. On 17 January 2012, Big Day Out organiser Ken West announced that the Auckland Big Day Out on 20 January 2012, would be the last Big Day Out in New Zealand, and that they will be putting on the festival in Australia only in 2013.