Formed in 1996 in Minneapolis, members of the band are David King (drums), Michael Lewis (saxophones) and Erik Fratzke (electric bass).
All three members compose music for the group; which places equal emphasis on improvisation. Happy Apple plays a unique brand of jazz music, drawing on several other genres; the group's members play in other bands ranging from indie rock and heavy metal to free jazz and electronic. The best known of these is The Bad Plus, in which King also plays drums.
Their name comes from a Fisher-Price toy from the sixties, which King often uses as an auxiliary percussion instrument.