The Dark Side of the Moon is the sixth studio album by English progressive rock group Pink Floyd, and was released in March 1973. The concept album built on ideas explored by the band in their live shows and earlier recordings, but it lacks the extended instrumental excursions that characterised their work following the departure in 1968 of founding member, principal composer, and lyricist Syd Barrett. The Dark Side of the Moon's themes include conflict, greed, the passage of time and mental illness, the latter partly inspired by Barrett's deteriorating mental state.