"21 Guns" is a song by American rock band Green Day. It was released as the second single from their eighth studio album, 21st Century Breakdown (2009), and serves as the sixteenth track from the album. The single was released through Reprise Records on May 25, 2009 as a digital download and July 14, 2009 as a CD single.

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.