Joe 90 is a 1968–1969 British science-fiction television series created by Gerry and Sylvia Anderson and filmed by their production company, Century 21, for ITC Entertainment. It follows the exploits of nine-year-old schoolboy Joe McClaine, who becomes a spy after his adoptive father invents a device capable of recording expert knowledge and experience and transferring it to another human brain. Armed with the skills of the world's top academic and military minds, Joe is recruited by the World Intelligence Network (WIN) as its "Most Special Agent".

First broadcast on the ITV regional franchises between 1968 and 1969, the 30-episode series was the sixth and last of the Andersons' productions to be made primarily using a form of marionette puppetry dubbed "Supermarionation". Their final puppet series, The Secret Service, would include extensive footage of live actors. As in the preceding series, Captain Scarlet and the Mysterons, the puppets of Joe 90 are of natural body proportions as opposed to the caricatured design used for Thunderbirds and earlier Supermarionation productions.

Though not as successful as Century 21's earlier efforts, Joe 90 has been praised for the characterisation of its main puppet cast and the quality of its scale model sets and special effects. Commentators have interpreted the spy-fi theme and use of a boy protagonist as both a "kids-play-Bond" concept and an enshrinement of children's imagination. The series has drawn some criticism for its lack of female characters, especially when compared to earlier Supermarionation productions.

As with its earlier productions, Century 21 produced tie-ins from comic strips to toy cars. The series was syndicated in the United States in 1969, repeated in the UK in the 1990s and released on DVD in the 2000s. A live-action film adaptation has been proposed more than once but remains undeveloped.