Bantam (in the USA) and HarperCollins Voyager (in the UK) released A Knight of the Seven Kingdoms today.
This book is a collection of George R.R. Martin's three Dunk and Egg novellas, short novels spanning a period of time beginning eighty-nine years before the events of A Game of Thrones and expected to conclude approximately fifty years later. The series chronicles the adventures of Ser Duncan the Tall, a hedge knight who rises from obscurity to great fame and high office, and his squire "Egg", who is more than he seems.
The collection consists of The Hedge Knight (1998), The Sworn Sword (2002) and The Mystery Knight (2010). Martin is working on the fourth story in the series, which has the working (but not final) title of The She-Wolves of Winterfell, but he decided some time ago to rework the story. It will not be released until after The Winds of Winter comes out. A working title of the planned fifth story in the series, The Village Hero, has also been disclosed. Martin has said there may be up to a dozen of these stories in total. Existing Song of Ice and Fire characters have appeared in the Dunk and Egg books, such as a very young Walder Frey, whilst Aemon Targaryen has been mentioned, but as the novellas progress and get closer to the present other characters are likely to appear. Fan speculation is high that the final story will take place at Summerhall on the fateful night of Prince Rhaegar Targaryen's birth.
Of course, in the meantime Martin does have two rather large novels to finish.