"Circus" is a song by American singer Britney Spears. It was released on December 2, 2008, through Jive Records as the second single from her sixth studio album of the same name. Written by Dr. Luke, Claude Kelly and Benny Blanco, "Circus" is a metaphor for the public's perception of Spears' life. After she listened to the track for the first time, she felt inspired to create an album and a tour with a circus theme. "Circus" is an uptempo electropop and dance-pop song with elements of pop rock and "half-rapped" vocals. The song's lyrics talk about being an entertainer and putting on shows.

The Circus Starring Britney Spears, commonly referred to as the Circus Tour, was the seventh concert tour by American entertainer Britney Spears. It was launched in support of her sixth studio album, Circus (2008). Rumors of a tour arose as early as October 2007, however, nothing was confirmed until December 2008, when the tour was officially announced, with North American and European dates revealed. The stage was composed of three rings and set in-the-round to resemble an actual circus. Fashion designers Dean and Dan Caten created the costumes. A giant cylinder screen was set above the stage to showcase videos and backdrops. Effects were provided by Solotech. Magician Ed Alonzo joined Spears during the second act. The setlist was composed generally from her albums In the Zone, Blackout and Circus. Spears announced she would tour Australia for the first time in June 2009.