A Warning to the Curious is a short film, the second of the British supernatural anthology series A Ghost Story for Christmas. Written, produced, and directed by the series' creator, Lawrence Gordon Clark, it is based on the ghost story of the same name by M. R. James, first published in the collection A Warning to the Curious and Other Ghost Stories (1925) and first aired on BBC1 on 24 December 1972. At 50 minutes it is the longest instalment in the series' original run.

It stars Peter Vaughan as Paxton, an amateur archaeologist whose attempt to track down one of the three legendary crowns of East Anglia causes him to be followed by the ghost of its last guardian, William Ager (John Kearney). He seeks the assistance of the vacationing scholar Dr. Black (Clive Swift) in order to return the crown and end the haunting.

Since airing, the episode has received critical acclaim as one of the best in the series, and one of the greatest works of horror television ever made. It was the last to be written and produced by Clark under the BBC Documentary Unit; starting with the following year's "Lost Hearts", the series would be produced by Rosemary Hill under the Drama Department, and other writers would be brought in. Though the series is traditionally regarded as airing on Christmas Eve, this was the last episode to do so until Whistle and I'll Come to You (2010).