Neela Debnath in The Independent:
The eagerly anticipated companion guide to George RR Martin's A Song of Ice and Fire series has finally arrived. While it may not be as chunky as the original novels, The World of Ice & Fire: The Untold History of Westeros and A Game of Thrones, it is just as rich and comprehensive. Martin, along with his co-authors, offers readers a breathtakingly detailed history of Westeros preceding the events in the novels. From the Dawn Age all the way through to the Glorious Reign, every entry is like embarking on a new journey through Martin's world. It's safe to say that Martin's world is more fully realised than JK Rowling's magical universe of Harry Potter and even JRR Tolkien's Middle-earth. In fact, many of the chapters could form their own series of equally weighty books. Both die-hard fans of the HBO adaptation, Game of Thrones, and A Song of Ice and Fire purists can appreciate this guide. Saying this, it is probably a little bit too geeky and information-overload for fans of the TV show.
Those who have already devoured Martin's monstrous novels will find this guide easier to digest. Subjects that are touched upon in the original books are explored here more thoroughly. The colourful chapters on the monarchs of Westeros read like something from the annals of long-dead tyrannical British monarchs – and it's great. For instance, Maegor the Cruel has a whole entry devoted to his life and reign. From the number of mistresses he had (each one has their own profile) to his mysterious death, Maegor's entry is certainly thorough. There are also smaller nuggets. Tywin Lannister is a looming presence in the novels but here he is shown in a new light. Yes, he's a schemer seeking power but he has a softer side when it comes to his wife, Joanna.