Green Day is a music group.
Green Day . For much of the group 's career , the band has been a trio with drummer Tré Cool , who replaced former drummer John Kiffmeyer in 1990 prior to the recording of the band 's second studio album , Kerplunk ( 1991 ) . The band 's eighth studio album , 21st Century Breakdown , was released in 2009 and achieved the band 's best chart performance to date .