Starting with the 2005 revival, the production team abandoned the traditional serial format for a largely self-contained episodic format with occasional multi-part stories and loose story arcs.Due to the BBC's 1970s junking policy, 97 episodes from the 1960s are missing, with the result that 26 serials are incomplete, although all of these still exist as audio recordings, and some have been reconstructed.
The practice of individually titled episodes resurfaced with the show's 2005 revival, when Doctor Who serial nature was abandoned in favour of an episodic format.
The story numbers are not official designations but are merely to serve as a guide to where the story stands in the overall context of the programme.
There is some dispute about, for example, whether to count Season 23's The Trial of a Time Lord as one or four serials, The first incarnation of the Doctor was portrayed by William Hartnell.
During Hartnell's tenure, the episodes were a mixture of stories set on earth of the future with extraterrestrial influence, on alien planets and in historical events without extraterrestrial influence, such as Marco Polo, one of the lost serials.
In his last story, The Tenth Planet, the Doctor gradually grew weaker to the point of collapsing at the end of the fourth episode, leading to his regeneration.
John Wiles replaced Verity Lambert as producer after Mission to the Unknown.
Innes Lloyd, in turn, replaced Wiles after The Ark.
Donald Tosh continued as script editor until The Massacre of St Bartholomew's Eve, which was also script-edited by his replacement, Gerry Davis.
, 826 episodes of Doctor Who have aired, concluding the ninth series.
This includes one television movie, and encompasses 263 stories over 35 seasons.
Additionally, four charity specials and two animated serials have also been aired.