John Glascock (2 May 1951 – 17 November 1979) was a British bass guitarist and singer. Glascock was best known for being the bassist and occasional lead vocalist of the rock band Carmen from 1972 to 1975 as well as 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.
In a September 1978 Guitar Player interview, Ritchie Blackmore had said "... John Glascock is a brilliant bass player, the best in the business in rock."