Green Day is a music band.
Green Day is an American punk rock band formed in 1986 by lead vocalist and guitarist Billie Joe Armstrong and bassist Mike Dirnt . The band 's rock opera , American Idiot ( 2004 ) , reignited the band 's popularity with a younger generation , selling six million copies in the U.S. . Punk rock ( or simply `` punk '' ) is a rock music genre that developed in the early to mid-1970s in the United States , United Kingdom , and Australia .