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Episodes

Doctor Who originally ran for 26 seasons on BBC One, from 23 November 1963 until 6 December 1989. During the original run, each weekly episode formed part of a story (or "serial")—usually of four to six parts in earlier years and three to four in later years. Some notable exceptions were: The Daleks' Master Plan, which aired twelve episodes (plus an earlier one-episode teaser, " Mission to the Unknown ", featuring none of the regular cast); almost an entire season of seven-episode serials (season 7); the ten-episode serial The War Games; and The Trial of a Time Lord, which ran for fourteen episodes (albeit divided into three production codes and four narrative segments) during season 23. Occasionally, serials were loosely connected by a story line, such as season 8 focusing on the Doctor battling a rogue Time Lord called the Master, season 16 's quest for the Key to Time, season 18 's journey through E-Space and the theme of entropy, and season 20 's Black Guardian trilogy.

The programme was intended to be educational and for family viewing on the early Saturday evening schedule. It initially alternated stories set in the past, which taught younger audience members about history, and with those in the future or outer space, focusing on science. This was also reflected in the Doctor's original companions, one of whom was a science teacher and another a history teacher.

However, science fiction stories came to dominate the programme, and the history-oriented episodes, which were not popular with the production team, were dropped after The Highlanders (1967). While the show continued to use historical settings, they were generally used as a backdrop for science fiction tales, with one exception: Black Orchid (1982), set in 1920s England.

The early stories were serialised in nature, with the narrative of one story flowing into the next and each episode having its own title, although produced as distinct stories with their own production codes. Following The Gunfighters (1966), however, each serial was given its own title, and the individual parts were assigned episode numbers.

Of the programme's many writers, Robert Holmes was the most prolific, while Douglas Adams became the best known outside Doctor Who itself, due to the popularity of his Hitchhiker's Guide to the Galaxy works.

The serial format changed for the 2005 revival, with what was now called a series usually consisting of thirteen 45-minute, self-contained episodes (60 minutes with adverts, on overseas commercial channels) and an extended 60-minute episode broadcast on Christmas Day. This system was shortened to twelve episodes and one Christmas special following the revival's eighth series, and ten episodes from the eleventh series. Each series includes standalone and multiple episodic stories, often linked with a loose story arc resolved in the series finale. As in the early "classic" era, each episode has its own title, whether stand-alone or part of a larger story. Occasionally, regular-series episodes will exceed the 45-minute run time; notably, the episodes " Journey's End " from 2008 and " The Eleventh Hour " from 2010 were longer than an hour.

883 Doctor Who instalments have been televised since 1963, ranging between 25-minute episodes (the most common format for the classic era), 45/50-minute episodes (for Resurrection of the Daleks in the 1984 series, a single season in 1985, and the most common format for the revival era since 2005), two feature-length productions (1983's " The Five Doctors " and the 1996 television film), twelve Christmas specials (most of approximately 60 minutes' duration, one of 72 minutes), and four additional specials ranging from 60 to 75 minutes in 2009, 2010, and 2013. Four mini-episodes, running about eight minutes each, were also produced for the 1993, 2005, and 2007 Children in Need charity appeals, while another mini-episode was produced in 2008 for a Doctor Who –themed edition of The Proms. The 1993 two-part story, entitled Dimensions in Time, was made in collaboration with the cast of the BBC soap-opera EastEnders and was filmed partly on the EastEnders set. A two-part mini-episode was also produced for the 2011 edition of Comic Relief. Starting with the 2009 special " Planet of the Dead ", the series was filmed in 1080i for HDTV and broadcast simultaneously on BBC One and BBC HD.

To celebrate the 50th anniversary of the show, a special 3D episode, " The Day of the Doctor ", was broadcast in 2013. In March 2013, it was announced that Tennant and Piper would be returning and that the episode would have a limited cinematic release worldwide.

In June 2017, it was announced that due to the terms of a deal between BBC Worldwide and SMG Pictures in China, the company has first right of refusal on the purchase for the Chinese market of future series of the programme until and including Series 15.