The Silmarillion is the 1977 posthumous book edited by Christopher Tolkien that presents the mythology behind J.R.R. Tolkien’s later stories.
Tolkien died in 1973, leaving extensive manuscripts in different forms and stages of completion. His son Christopher edited and arranged material for publication, with assistance from Guy Gavriel Kay. The Silmarillion appeared in 1977 and gathers creation stories, accounts of the First Age, the history of Númenor, and events leading toward The Lord of the Rings.
The book is structured as several related sections. The Ainulindalë describes creation, the Valaquenta introduces the Valar and Maiar, and the Quenta Silmarillion tells the central story of the Silmarils and the wars against Morgoth.
It is not a conventional single novel. Its materials span decades of Tolkien’s writing and sometimes preserve different versions of events. Unfinished Tales, published later, is another posthumous collection, but it has a different editorial purpose and title.