Shada is a story from the British science fiction television series Doctor Who. Written by the series' script editor Douglas Adams, it was intended as the final serial of the 1979–80 season (season 17) but was never originally completed, owing to strike action at the BBC during studio recording. Entering production as a six-part story (6 x 25-minute episodes) in 1979, plans were later revised for the story to be broadcast as a four-part story (4 x 25-minute episodes) in 1980. Ultimately however, the story was never completed in either format.

The BBC released a completed version of Shada in 2017, with missing dialogue newly recorded by the original cast, using the same audio equipment employed in the initial shoot, and animated by the team that undertook the reconstruction of the 1966 serial The Power of the Daleks. This version was released on DVD and Blu-ray in 2017, and finally broadcast on television as a feature length TV movie – which was titled The Lost Episode rather than Shada – in 2018.

A new version with enhanced animation and split into six episodes was released on 20 December 2021, as part of a Season 17 Blu-ray boxset.

Previous attempts to present the story include a narrated reconstruction for BBC Video; a re-imagined audio play by Big Finish Productions, also offered with basic Flash imagery on BBCi and the BBC's Doctor Who website; and a novelisation by Gareth Roberts, based on the latest shooting scripts, with the author's own additions.