21st Century Breakdown is the eighth studio album by the American rock band Green Day, released on May 15, 2009, through Reprise Records. Green Day commenced work on the record in January 2006 and forty-five songs were written by vocalist and guitarist Billie Joe Armstrong by October 2007, but the band members did not enter studio work until January 2008.

Green Day is an American rock band formed in the East Bay of California in 1987 by lead vocalist and guitarist Billie Joe Armstrong and bassist and backing vocalist Mike Dirnt, with drummer Tré Cool joining in 1990. In 1994, their major-label debut Dookie, released through Reprise Records, became a breakout success and eventually shipped over 10 million copies in the U.S. Alongside fellow California punk bands Bad Religion, the Offspring, Rancid, NOFX, Pennywise and Social Distortion, Green Day is credited with popularizing mainstream interest in punk rock in the U.S.