The song was conceived and written as a tribute and remembrance to their former band member Syd Barrett, a founding member of Pink Floyd. Barrett was ousted from the band by the other members in 1968 due to his drug use and troubled mental health, which had affected his ability to integrate with the rest of the band and perform and create as a musician. He was replaced by David Gilmour, Barrett's former school friend who had initially been brought in as second guitar.
The remaining band members felt guilty for removing him, but they viewed it as necessary, admiring Barrett's creativity and being concerned about his severe mental decline. The work was first performed on their 1974 French tour and recorded for their 1975 concept album Wish You Were Here. It was intended to be a side-long composition (like "Atom Heart Mother" and "Echoes") but was split into two sections and used to bookend the album, with new material composed that was more relevant to the album and to the situation in which the band found themselves.
All nine parts of Shine On You Crazy Diamond, which is one of the greatest pieces of music made. This composition was a tribute to former band member, Syd Barrett. Written and performed by Roger Waters, David Gilmour and Richard Wright. From the album "Wish You Were Here".