Captain Scarlet and the Mysterons, often shortened to Captain Scarlet, is a British science fiction television series created by Gerry and Sylvia Anderson and filmed by their production company Century 21 for ITC Entertainment. It is the sixth Anderson series to be filmed using a form of electronic marionette puppetry dubbed "Supermarionation" combined with scale model special effects. Running to thirty-two 25-minute episodes, it was first broadcast on ITV regional franchises between 1967 and 1968 and has since aired in more than 40 other countries, including the United States, Canada, Australia, New Zealand and Japan.

Set in 2068, Captain Scarlet presents a "war of nerves" between Earth and the Mysterons, a race of Martians who possess partial control over matter. When a misunderstanding causes human astronauts to attack their city on Mars, the Mysterons swear revenge and launch reprisals against Earth. These are countered by Spectrum, a worldwide security organisation. In the first episode, Spectrum agent Captain Scarlet acquires the Mysterons' self-healing power of "retrometabolism" and is rendered "indestructible", being able to recover from injuries that would normally be fatal. Scarlet immediately becomes Spectrum's top asset in its fight against the Mysterons.

Captain Scarlet, the eighth of the Andersons' ten puppet series, was preceded by Thunderbirds and followed by Joe 90 and The Secret Service. In terms of visual aesthetic, it marked a departure from earlier series in its use of puppets that were sculpted to realistic body proportions. Repeated several times in the UK, it has generated tie-ins ranging from toy cars and action figures to audio plays and novels, as well as strips in the weekly children's comic TV Century 21.

Compared to earlier Anderson productions, Captain Scarlet is widely regarded as "darker" in tone and less suited to children because of its violent content, as well as its themes of alien aggression and interplanetary war. The change in puppet design has divided opinion and the decision to make the protagonist "indestructible" has been brought into question. The series has been praised for its use of a multinational, multiethnic puppet cast and depiction of a utopian future Earth. A computer-animated remake, New Captain Scarlet, first aired in 2005.