The Silmarillion was published posthumously in 1977 as a collection of Middle-earth myths.
J.R.R. Tolkien worked on the stories and histories that became The Silmarillion for much of his life, but he did not complete and publish the book himself. His son Christopher Tolkien edited material from the manuscripts and arranged it for publication four years after Tolkien’s death. The resulting volume was released on 15 September 1977.
The book describes the creation of the world, the early history of the Elves, the wars against Morgoth, and later events that lead toward the age of The Hobbit and The Lord of the Rings. It is more like a mythology and historical record than a single continuous adventure novel.
Readers sometimes confuse The Silmarillion with Unfinished Tales, another posthumous collection edited by Christopher Tolkien. The Silmarillion is the major published account of Tolkien’s deep history of Arda, while Unfinished Tales gathers separate narratives and incomplete texts.