Big Brother 2008, also known as Big Brother 9, was the ninth series of the British reality television series Big Brother, that aired on Channel 4 and E4. The series launched on 5 June 2008, and ran for 13 weeks until 5 September 2008.

The winner of was Rachel Rice, who beat bookies' favourite Michael Hughes in the final vote with 51.3%. At the time of the series, Big Brother 9 was the least watched summer series in Big Brother's history, until the following series, with an average of only 3.6 million, down on Big Brother 8's by 0.3m.

No housemates in this series were represented in Ultimate Big Brother, a mini-series to mark the end of Big Brother on Channel 4. However Rex, Kathreya and Stuart entered to take part in tasks.