UFO is a British television science fiction series created by Gerry Anderson and Sylvia Anderson and produced by the Anderson's and Lew Grade's Century 21 Productions for Grade's ITC Entertainment company. The Andersons had previously made a number of very successful marionette-based children's science fiction series including Stingray, Thunderbirds, and Captain Scarlet. They had also made one live-action science fiction movie, Doppelgänger, also known as Journey to the Far Side of the Sun, and now felt ready to move into live-action television and aim at a more adult market.

UFO was the Andersons' first totally live-action TV series. Despite the assumption of many TV station executives, the series was not aimed at children, but deliberately sought an older audience; many episodes featured adult themes such as adultery, divorce, and drug use.

UFO first aired in the UK in 1970 and in US syndication over the next two years. In all, 26 episodes, including the pilot, were filmed over the course of more than a year, with a five-month production break caused by the ultimate closure of the MGM-British Studios in Borehamwood, where the show was initially made. It is currently airing in the US in remastered HD on Voom HD Networks' Family Room HD.

An idiosyncrasy of the series is that the term "UFO" is pronounced as a word ("you-foh"), as suggested by the real-world originator of the term Edward J. Ruppelt, and not as the more common "you-eff-oh". This is particularly true of the lead character, Ed Straker. Technically speaking the series title should properly be pronounced "you-foh" as well. However, the "you-foh" pronunciation was not consistently applied and some supporting characters use the more traditional form.

In a sad coincidence, lead actors Ed Bishop and Michael Billington died in June 2005, within five days of each other.

In the year 1980 the Earth is threatened by an alien race who kidnap and kill humans and use them for body parts. A highly secret military organization is set up in the hope of defending the Earth from this alien threat. This organization is named SHADO (Supreme Headquarters Alien Defence Organization) and operates from a secret location beneath a film studio. They also operate a fleet of submarines and have a base on the moon as well as an early warning satellite that detects inbound UFOs. UFOs can be destroyed in space by Interceptors which are launched from Moonbase. If one gets through it can be attacked in the Earth's atmosphere by a high altitude aircraft launched from one of the submarines. If a UFO also avoids this and manages to land it can be tracked and destroyed by a number of Mobiles (armored vehicles) which are deployed throughout the world. Written by Kevin Steinhauer