Season 4 of Game of Thrones was formally commissioned by HBO on 2 April 2013, following a substantial increase in audience figures between the second and third seasons. However, substantial pre-production work on the season had already taken place previously to this point, including the writing of at least six of the scripts (by March 2013), and the booking of some of the filming dates. The season will be produced in the second half of 2013 and air in the first half of 2014. David Benioff and D.B. Weiss are to return as showrunners, having signed a new two-year contract with HBO prior to the commissioning of the third season.
Season 4 will be based on the later part of A Storm of Swords, the third book in the A Song of Ice and Fire series by George R.R. Martin. Whilst the first two seasons were roughly based on the first two books in the series, the sheer length of the third novel in the series (half again the length of the first novel by word-count) made this impractical. It is unclear if the potential fourth season will feature events purely from the third book, or if events from the opening of the fourth and fifth novels (which run concurrently alongside one another and the very end of the third book) would also be featured. Martin wrote in a commentary on his blog that the most of fourth season will be drawn from the third book, but also some material may be added from the fourth and fifth book.
It has been confirmed that the production will return to Dubrovnik (King's Landing) in Croatia, while it is assumed that filming will also continue in Northern Ireland. Whether filming would also resume in Morocco (Slaver's Bay) and Iceland (Beyond the Wall) is not yet known.
All regular cast members whose characters survive the events of Season 3 are expected to return for the fourth season.
Casting for season 4 is underway, as confirmed by a leaked casting audition. Roles expected to be cast include
- David Benioff: executive producer.
- D.B. Weiss: executive producer. Benioff and Weiss signed a two-year contract in 2012, indicating that they will stay with the show to at least the end of the fourth season.