Big Brother is an American television reality competition show based on the Dutch reality show of the same name created by producer John de Mol Jr. in 1997. The series takes its name from the character in George Orwell's 1949 novel Nineteen Eighty-Four. The American series launched on July 5, 2000 on CBS and since the discontinuation of the Spanish version in 2022, is the longest-running adaptation in the Big Brother franchise.

The show broadly follows the premise of other versions, in which a group of contestants, known as "HouseGuests", live together in a specially constructed house that is isolated from the outside world for a cash prize of $750,000 ($500,000 prior to season 23). The Houseguests 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, Houseguests are evicted by being voted out of the competition.

In its inaugural season (which followed the original Dutch format and audience voting determined evictees and the eventual winner), ratings declined, and critical reaction grew increasingly negative, prompting the series to be revamped for the second season, which focused on competition and gameplay.

The show's twenty-sixth season premiered on July 17, 2024; its twenty-seventh season will premiere in the summer of 2025.

The show produced three spin-offs: Big Brother: Over the Top (which aired for one season and was the first reality game show to air exclusively on a streaming platform, in Fall 2016 on CBS' streaming service, CBS All Access), Celebrity Big Brother, which first aired on CBS in February 2018, and the Big Brother Reindeer Games, which aired for one season on CBS in December 2023.