"The Mysterons" is the first episode of Captain Scarlet and the Mysterons, a British 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 Desmond Saunders, it was first officially broadcast on 29 September 1967 on ATV Midlands, although it had received an unscheduled test screening in the London area five months earlier.

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. 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. 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.