The Thirty Nine Steps is a British 1978 thriller film directed by Don Sharp, with screenplay by British playwright Michael Robson, based on the novel The Thirty-Nine Steps by John Buchan. It was the third film version of the 1915 novel.

This version of Buchan's tale stars Robert Powell as Richard Hannay, Karen Dotrice as Alex, John Mills as Colonel Scudder, and a host of other well-known British actors in smaller parts. It is generally regarded as the closest to the novel, being set before the Great War. The early events and overall feel of the film bear much resemblance to Buchan's original story, albeit with a few changes such as the re-casting of Scudder as a more immediately sympathetic character and the introduction of a love interest. It also introduces a different meaning for the "thirty-nine steps", although unlike its filmed predecessors it returns to Buchan's original notion of being an actual staircase. It is known for the Big Ben sequence near the end, inspired by the film My Learned Friend (1943) starring Will Hay, although this is its most fundamental deviation from Buchan's original story, which reaches its culmination in a coastal location in Kent.

Powell later reprised the role in the ITV series Hannay which ran for 13 episodes from 1988 to 1989.