Green Day is an American rock band formed in 1989. The band consists of three core members: Billie Joe Armstrong (guitar, lead vocals), Mike Dirnt (bass) and Tre Cool (drums).

Green Day was originally part of the punk rock scene at 924 Gilman Street in Berkeley, California. Its early releases for independent label Lookout! Records earned them a grassroots fanbase, some of whom felt alienated when the band signed to a major label. Nevertheless, its major label debut Dookie became a breakout success in 1994 and eventually sold over 10 million copies in the U.S. alone. As a result, Green Day was widely credited, along with fellow California punk bands The Offspring and Rancid, with reviving mainstream interest in and popularizing punk rock in the United States. Green Day's immediate follow-up albums did not achieve the massive success of Dookie, but they were still relatively successful. Its 2004 rock opera American Idiot reignited the band's popularity with a younger generation, selling 5 million copies in the U.S.