"Know Your Enemy" is the first single from Green Day's eighth studio album, Know Your Enemy, which was released on April 16th, 2009 from Reprise Records.

Alternative Press called the song a "huge rocker" which is a "fierce call to arms against apathy." It was also referred to as sounding "like an out-take from the Dookie sessions." About.com's Bill Lamb said the song was "not a stroke of genius" and was not on par with their last album, but said it was a "great appetizer" for one of the most eagerly awaited albums of 2009.

Billie Joe Armstrong told Q magazine: “It’s a rallying song. It’s about liberating yourself from a lot of bullshit that you see on TV.”

A music video for this song will air on April 24, 2009. It will be the first global cross-channel video première for MTV and VH1 networks. It is directed by Motion Theory's Matthew Cullen.

The first play of song occurred on Sara Cox's BBC Radio 1 show at 10:00AM GMT. 93.3 WMMR debuted the song on the 'Preston and Steve show' at 7:05AM. A 90 second clip of the band playing the song was featured at the opening teaser of the NCAA 2009 Men's Basketball Championship game on April 6, 2009. The 90-second clip featured scenes from the music video intercut with scenes from the basketball season. The clip is now available for view on both YouTube and the official Green Day website, after being put up and taken down repeatedly. A short preview clip can be found on Green Day's official website. It was made available for internet download on April 16, 2009. In addition, a 90 second clip of the song was posted on the bands' MySpace page on April 6, 2009