Nightcap: The Unreleased Masters 1973–1991 is a double compilation album by British rock band Jethro Tull, released on 22 November 1993.

The songs "Scenario", "Audition" and "No Rehearsal" initially appeared on the 20 Years of Jethro Tull box set as a single track entitled "The Chateau d'Isaster Tapes".

The material on the first disc was mixed and arranged as the aforementioned three tracks were on the 20 Years box set with numerous flute overdubs by Ian Anderson, but excludes the songs "Big Top" and "Sailor".

This includes the same mixes as on the A Passion Play book set but with a stripped down version of "The Story of the Hare Who Lost His Spectacles" inserted in its original position.

Many of the songs on this disc also appear as bonus tracks on CD reissues of Jethro Tull studio albums.