Prequel

The "prequels" are a series of prologues to certain episodes of Doctor Who from series 6, 7 and 9, and around the 50th anniversary special. They are released by the BBC on their official site. They can be compared to the Tardisodes produced for series 2. Note that, while some were indeed released after the episode in question, for the most part they were released some time shortly prior to their TV stories, so the term ‘prequel’ is technically misnomer, since a ‘prequel’ is by definition set before but released after the production in relation. However, the term is used here as it is the BBC’s only official title on offer for this specific series.

Series 6

 * A prequel to The Impossible Astronaut
 * A prequel to The Curse of the Black Spot
 * A prequel to A Good Man Goes to War
 * A prequel to Let's Kill Hitler
 * A prequel to The Wedding of River Song

Series 7

 * A prequel to The Doctor, the Widow and the Wardrobe was released online prior to the airing of the special.
 * The Asylum of the Daleks Prequel, a prequel to Asylum of the Daleks, was released online prior to the airing of the episode. A series of mini-episodes, Pond Life, also acted as a prequel to this story.
 * The Making of the Gunslinger, a prequel to A Town Called Mercy.
 * The Snowmen also had two different prequels. The first, The Great Detective, was given a television broadcast as part of the 2012 Children in Need event, while the second, Vastra Investigates: A Christmas Prequel, was released online the following month.
 * The Bells of Saint John: A Prequel, a prequel to The Bells of Saint John, was released online prior to the airing of the episode.
 * Another prequel, entitled The Battle of Demons Run: Two Days Later, was released in the build-up to this episode, though it detailed the events which took place just after A Good Man Goes to War and did not directly relate to events or characters from The Bells of Saint John, acting more as another prequel to The Snowmen.
 * She Said, He Said: A Prequel and Clarence and the Whispermen were prequels to the Series 7 finale, The Name of the Doctor.

50th anniversary

 * The Night of the Doctor and The Last Day were prequels to The Day of the Doctor.

Series 8

 * A prequel to Deep Breath was shown at cinema screenings of the episode.

Series 9

 * Prologue and The Doctor's Meditation were prequels to The Magician's Apprentice.

Introductions

 * Ian Chesterton: An Introduction - introduction to The Crusade
 * Cinema Introduction - intro to The Day of the Doctor

Home video releases

 * The prequels for The Impossible Astronaut, The Curse of the Black Spot, A Good Man Goes to War, Let's Kill Hitler and The Wedding of River Song were released on the Complete Series 6 DVD and Blu-ray box set in November 2011.
 * The prequel for The Doctor, the Widow and the Wardrobe was released on the DVD and Blu-Ray of the story in January 2012, and on the Complete Series 7 DVD and Blu-ray box set in October 2013.
 * The prequels for Asylum of the Daleks and A Town Called Mercy were released on the Series 7: Part 1 DVD and Blu-ray box set in October 2012, and on the Complete Series 7 DVD and Blu-ray box set in October 2013.
 * The prequels for The Snowmen and The Bells of Saint John were released on the Series 7: Part 2 DVD and Blu-ray box set in May 2013, and on the Complete Series 7 DVD and Blu-ray box set in October 2013. Clarence and the Whispermen was also included.
 * The Battle of Demon's Run: Two Days Later and She Said, He Said were released on the Complete Series 7 DVD and Blu-ray box set in October 2013, along with all of the previously released Series 7 prequels.

Precuelas