Black Flag is an American hardcore punk band formed in 1976 in Hermosa Beach, California. The band was established by Greg Ginn, the guitarist, primary songwriter, and sole continuous member through multiple personnel changes in the band. They are widely considered to be one of the first hardcore punk bands. After breaking up in 1986, Black Flag briefly reunited in 2003 and again in 2013.

Black Flag's sound mixed the raw simplicity of the Ramones with atonal guitar solos and frequent tempo shifts. The lyrics were written mostly by Ginn, and like other punk rock bands of the late 1970s and early 1980s, Black Flag voiced an anti-authoritarian and non-conformist message, in songs punctuated with descriptions of social isolation, neurosis, poverty, and paranoia. These themes were explored further when Henry Rollins joined the band as lead singer in 1981. Most of the band's material was released on Ginn's independent label, SST Records.