The document discusses the origins and development of progressive and glitter rock in the late 1960s and 1970s. It was inspired by The Beatles' album Sgt. Pepper's Lonely Hearts Club Band and involved adding orchestral instruments and experimenting with classical forms and electronic music. Key progressive rock bands like The Moody Blues, Genesis, Jethro Tull, and Electric Light Orchestra incorporated orchestras into their music. Bands like Yes and Emerson, Lake & Palmer composed in classical structures and recorded versions of classical pieces.