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.

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.

Series 8

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

50th anniversary

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

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.

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