Big Brother 11 is the eleventh 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 series premiered on CBS on July 9, 2009, and lasted ten weeks until the live finale on September 15, 2009. The eleventh season saw a slight increase in ratings when compared to the past season of the series, which had some of the lowest ratings to date. The season premiered to a total of 6.59 million viewers, a slight increase from the previous season's launch. Despite this, it is the second lowest premiere for a season behind Big Brother 10. The season finale had a total of 7.78 million viewers, continuing to average slightly above the past season. In total, the series averaged 7.19 million viewers, higher than that of the previous two seasons. Big Brother 11 featured a total of 13 HouseGuests, one of which was a returning player from a previous season. The series ended after 73 days, in which HouseGuest Jordan Lloyd was crowned the winner and Natalie Martinez 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.