Thunderbird 6 is a 1968 British science fiction puppet film based on Thunderbirds, a Supermarionation television series created by Gerry and Sylvia Anderson and filmed by their production company Century 21 Productions. Written by the Andersons and directed by David Lane, it is the sequel to Thunderbirds Are Go (1966).

The film is largely set on Skyship One – a futuristic airship designed by Brains, the inventor of International Rescue's Thunderbird machines. The plot sees Alan Tracy, Tin-Tin Kyrano, Lady Penelope and Parker representing International Rescue as guests of honour on Skyship One's round-the-world maiden flight, unaware that master criminal The Hood is once again plotting to acquire the organisation's technological secrets. The Hood's agents murder the airship's crew and assume their identities to lure International Rescue into a trap. Meanwhile, Brains' efforts to design a proposed sixth Thunderbird collide with fate when Skyship One is damaged and its occupants' only salvation seems to be Alan's old Tiger Moth biplane.

Actors John Carson and Geoffrey Keen provided guest voices, with additions to the regular voice cast in the form of Keith Alexander and Gary Files. The puppet design compromised between the caricatures that Century 21 had used up until Thunderbirds Are Go and the realistically proportioned marionettes that were introduced in Captain Scarlet and the Mysterons. The film was shot between May and December 1967. Some of the sequences showing the Tiger Moth in flight were shot on location using a full-sized plane, but a legal dispute with the Ministry of Transport over alleged dangerous flying forced the crew to film the remaining shots in-studio with scale models.

Thunderbird 6 was released in July 1968 to a mediocre box office response that ruled out the production of further sequels. Critical response has remained mixed: while the special effects have been praised, the story polarised commentators.