Moonbase 3 is a British science fiction television series that ran for six episodes in 1973. It was a co-production between the BBC, 20th Century Fox and the American ABC network. Created by Doctor Who producer Barry Letts and script editor Terrance Dicks as a realistic alternative strand of TV science-fiction, it was not a commercial or critical success (Dicks himself has stated in a foreword to a collection of Tom Baker-era Doctor Who scripts that they "overdid the grimness and forgot about the sense of wonder that science fiction is all about").

It starred Donald Houston as Director David Caulder, who is appointed to the position after the previous director was killed while returning to Earth. Ralph Bates was Michel Lebrun, the deputy director, who was concerned about keeping to the rules. Fiona Gaunt played Doctor Helen Smith, the base's psychiatrist, and Barry Lowe played Tom Hill, the head of the base technical section.

The programme was notable for its combination of realistic spaceflight procedures, ensured by hiring BBC technical adviser James Burke, and its strong character-based writing. Although very dated in terms of its looks and assumptions about the future, it remains well regarded in retrospect.