Do Not Adjust Your Set is a British television series produced originally by Rediffusion, London, and then by the fledgling Thames Television for British commercial television channel ITV from 26 December 1967 to 14 May 1969. The show took its name from the message (frequently seen on the TV screen in those days) that was displayed when there was a problem with transmission or technical difficulties.

It helped launch the careers of Denise Coffey, David Jason, Eric Idle, Terry Jones and Michael Palin; the last three became members of the Monty Python comedy troupe soon afterward. Although originally conceived as a children's programme, it quickly acquired a fandom amongst adults, including future Python members John Cleese and Graham Chapman.

The Bonzo Dog Doo-Dah Band, a satirical comedy/art/pop group, also performed songs in each programme and frequently appeared as extras in sketches. The programme itself comprised a series of satirical sketches, often presented in a surreal, absurd and discontinuous style – anticipating Monty Python's Flying Circus, which began five months after the last episode of Do Not Adjust Your Set. Several surreal animations between sketches were crafted for the second series by Terry Gilliam, who soon graduated to Python along with Palin, Jones and Idle.

One recurring feature of the show was Captain Fantastic, a superhero parody featuring David Jason in farcical and morbid adventures against villainess Mrs. Black (Coffey). These segments were shot entirely on location in London. The feature was so popular with the young audience that after Do Not Adjust Your Set itself ended, Captain Fantastic briefly continued in its own capacity in the children's magazine show Magpie.

Only 14 of the original 29 episodes currently exist.