John Glascock (2 May 1951 – 17 November 1979) was a British musician. He was the bassist and occasional lead vocalist of the rock band Carmen from 1972 to 1975; and the bass guitarist for progressive rock band Jethro Tull from 1976 until his death in 1979. Glascock died at the age of 28 as a result of a congenital heart valve defect, which was worsened by an infection caused by an abscessed tooth.