Several portions of the long-running British science-fiction television programme Doctor Who are no longer held by the BBC. Between 1967 and 1978, the BBC routinely deleted archive programmes for various practical reasons—lack of space, scarcity of materials, and a lack of rebroadcast rights. As a result, 97 of 253 episodes from the programme's first six years are currently missing, primarily from seasons 3, 4 and 5, leaving 26 serials incomplete. Many more were considered lost until recovered from various sources, mostly overseas broadcasters.
