The Zygons are an extraterrestrial race in the long-running British science fiction television programme Doctor Who. The Zygons have shape-shifting abilities, allowing them to replicate the appearance of another being. Limited by the small size of their force, they rely on shape-shifting and their organic space craft to conceal their numbers and seize power on Earth. The Zygons were conceived by writer Robert Banks Stewart, and designed by James Acheson as part of a collaboration with John Friedlander. Then director Douglas Camfield also influenced the final appearance. They were designed to resemble "oversized embryos."

Terror of the Zygons is the first serial of the thirteenth season of the British science fiction television series Doctor Who, which was the first broadcast in four weekly parts on BBC1 from 30 August to 20 September 1975. The serial featured the last regular appearance by Ian Marter as companion Harry Sullivan and Nicholas Courtney as Brigadier Lethbridge-Stewart.