The Edge Chronicles is a children's fantasy novel series written by Paul Stewart and Chris Riddell. It consists of four trilogies, plus four additional books, and other books related to the universe (The Edge). The series was originally published by Doubleday, a subsidiary of Penguin Random House, and has sold more than three million copies, according to its publisher.The stories of The Edge Chronicles take place in the fictional world of The Edge, a vast cliff with no apparent bottom. The majority of books are grouped into sagas, with each saga focusing on one character. The series covers a 600-year period, divided into three "Ages of Flight". In The first age, floating rocks were used to stay airborne but then stone sickness, which made the rocks crumble, hit. Then, floating wood was used, and finally phrax-power. The power of flight is a major theme of the books, with each age defined by the current technology used for air travel. The series is notable for its flora and fauna, along with the maps of various locations in The Edge.The first three trilogies were released over the course of 1998 to 2006, with a standalone saga serving as a conclusion to the first two ages of flight and a beginning to the third released in 2009. The series was planned to end after the tenth book, with the author's blog, Weird New Worlds serving as the continuous adventures with weekly 'chapter' installments. After the completion of the 66 chapters of the blog, the authors decided to revisit the series with the fourth trilogy which would adapt the characters and stories from the blog, with the first and second books released in 2014 and 2015 respectively. The series also includes a number of short stories, along with a companion book. Source: Wikipedia (en)