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.

William Hartnell continues his journey as The First Doctor, accompanied by companions Vicki (Maureen O'Brien) and Steven Taylor (Peter Purves).

In the final story The War Machines, Dodo also departs, and the Doctor was joined by Polly (Anneke Wills) and Ben (Michael Craze).

Peter Butterworth makes his second and final appearance as the Meddling Monk in the serial The Daleks' Master Plan, though his presence in the story is limited to three parts only; "Volcano", "Golden Death", and "Escape Switch".

[citation needed] Four of the stories from Season 3 ("Mission to the Unknown", The Myth Makers, The Massacre, and The Savages) are completely missing from the BBC archive, with no surviving episodes.

"Mission to the Unknown", however, is unique in that it is the only missing episode of Doctor Who to be fully recreated in live-action, with the student-made project having its production quality on par with that of 1960s television.