The Ark is the sixth serial of the third season of the British science fiction television series Doctor Who, which was first broadcast in four weekly parts from 5 to 26 March 1966.

The third season of British science fiction television series Doctor Who began on 11 September 1965 with the story Galaxy 4 and ended on 16 July 1966 with The War Machines. Only 17 out of 45 episodes survive in the BBC archives; 28 remain missing. As a result, only three serials are complete.