Black Flag was an American rock band formed in 1977 in Hermosa Beach, California. The band was established largely as the brainchild of Greg Ginn: the guitarist, primary songwriter and sole continuous member through multiple personnel changes. They are widely considered to be one of the first hardcore punk bands alongside Middle Class, Bad Brains, Discharge and Minor Threat.

Black Flag forged a unique sound early on that mixed the raw simplicity of the Ramones with atonal and microtonal guitar solos and frequent tempo shifts. The band was also known for the intense and evocative lyrics found in their songs, most of which were penned by Ginn. Like other punk bands of this era, Black Flag gave voice to an anti-authoritarian, non-conformist message, featuring songs punctuated with descriptions of isolation, neurosis, poverty, and paranoia, themes that would be explored further when Henry Rollins joined the group as lead singer in 1981. Most of the band's material was released on Ginn's independent label, SST Records.