Celebrity Big Brother is a British television reality game show based on the Dutch show Big Brother, created by producer John de Mol Jr. in 1997, which aired from 2001 to 2018, and again since 2024. The show follows a number of celebrity contestants, known as housemates, who were isolated from the outside world for an extended period of time in a custom built house. Each week, one of the housemates is evicted by a public vote, with the last housemate named the winner. The series takes its name from the character in George Orwell's 1949 novel Nineteen Eighty-Four.

Celebrity Big Brother began as a one-time spin-off series to the original Big Brother UK, and premiered on Channel 4 on 9 March 2001. Following the successful first series, the show returned the following year for a second series. Though the show did not air for the next two years, it returned in 2005 and 2006. Following the highly controversial fifth series in 2007, the show did not return in 2008. It did air in 2009, but it was officially axed after the seventh series in 2010 when Channel 4 chose to cancel the programme as well as the main series. Despite this, it was picked up by Channel 5, and Celebrity Big Brother returned in 2011. Between 2012 and 2018, two editions of Celebrity Big Brother aired each year, with one airing in January and one airing following the conclusion of the civilian series in August. The show was initially hosted by Davina McCall from its inception to its cancellation by Channel 4. Despite being offered the position of host following the show's move to Channel 5, McCall chose not to return. Brian Dowling, who had won on Big Brother 2 and Ultimate Big Brother, replaced McCall as the host of the series. Dowling hosted the eighth to eleventh series, before being replaced by Emma Willis from the twelfth series until the show's cancellation on Channel 5 following the twenty-second series. Following the show's relaunch on ITV in March 2024, AJ Odudu and Will Best will host the show from the twenty-third series onwards. Marcus Bentley has narrated the series since its inception in 2001.

Much like its predecessor, Celebrity Big Brother was met with commercial success and has also received extensive media coverage and publicity since it premiered. It has been covered in spin-off series such as Big Brother's Big Mouth and Big Brother's Bit on the Side, which also covered the main series. Similar to the parent series, Celebrity Big Brother has been the source of much controversy and criticism, most notably during the 2007 series. Following this, a spin-off series known as Big Brother: Celebrity Hijack aired in 2008 in the place of Celebrity Big Brother. It has been noted that numerous celebrities who have appeared on the series have become more prominent figures in the media than before.

On 14 September 2018, Channel 5 announced that Big Brother and Celebrity Big Brother would not be returning to the channel after the end of the nineteenth regular series. The twenty-second series of Celebrity Big Brother ended on 10 September 2018 and was the final series to air on Channel 5.

In August 2022, ITV plc announced that they were reviving Big Brother. The series relaunched in October 2023, which subsequently led to media speculation as to whether they would revive the celebrity version. In November 2023, ITV announced the relaunch of Celebrity Big Brother, beginning with the twenty-third series airing in March 2024 on ITV (ITV1 and STV).