Big Brother 5 is the fifth season of the American reality television series Big Brother. It is based upon the Netherlands series of the same name, which gained notoriety in 1999 and 2000. The season premiered on CBS on July 6, 2004, and lasted eleven weeks until the live finale on September 21, 2004. This season was the first to be accompanied by the House Calls: The Big Brother Talk Show spin-off series, which was viewable online and discussed the events of the game. The fifth season continued to have the ratings success of the previous season, averaging more than eight million viewers per episode. The Big Brother 5 premiere garnered 9.55 million viewers, almost matching that of the previous season's launch night. Ratings stayed gradually the same, with the finale receiving more than 10 million viewers. The season premiere currently has the third highest ratings for a premiere episode, only behind Big Brother 1 and Big Brother 4. Big Brother 5 featured a total of 14 HouseGuests, an increase from previous editions. The series ended after 82 days, in which HouseGuest Drew Daniel was crowned the Winner, and Michael Ellis the Runner-Up.

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.