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 Productions for distributor ITC Entertainment. Running to thirty-two 25-minute episodes, it was first broadcast on ITV regional franchises between 1967 and 1968 and has since been transmitted in more than 40 other countries, including the United States, Canada, Australia, New Zealand and Japan. It is one of several Anderson series that were filmed using a form of electronic marionette puppetry dubbed "Supermarionation" combined with scale model special effects sequences.

Set in 2068, Captain Scarlet follows the "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 vow 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 thus rendered "indestructible", being able to recover from otherwise fatal injuries. In this way, Scarlet 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 represents a departure from Thunderbirds in its use of non-caricatured puppets sculpted to realistic body proportions. Repeated several times in the UK, it has generated tie-ins from toy cars and action figures to audio plays and original novels, as well as strips in the weekly children's comic TV Century 21.

Compared to Thunderbirds, Stingray, and earlier Anderson productions, Captain Scarlet is generally considered "darker" in tone and less suited to child audiences due to its violent content and themes of alien aggression and interplanetary war. The change in puppet design has divided opinion, while the wisdom of making the protagonist "indestructible" has also been questioned. However, the series has been praised for its use of a multinational, multi-ethnic puppet cast and depiction of a utopian future Earth. A computer-animated reboot, New Captain Scarlet, was first broadcast in 2005.