Big Brother, also retrospectively known as Big Brother 1, was the first series of the British reality television series Big Brother. The show followed eleven 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 or more of the housemates were evicted by a public vote. The last remaining housemate, Craig Phillips, was declared the winner, winning a cash prize of £70,000.

The series lasted 64 days and was presented by Davina McCall. It launched on Channel 4 on 18 July 2000 and ended on 15 September 2000. Ten housemates entered on the first day, with one additional housemate being introduced in the sixth week. The series was watched by an average of 4.5 million viewers. It became the subject of intense press attention throughout its broadcast, and gained particular notoriety after one housemate, Nick Bateman, was ejected from the House for breaking the rules.