Which Tolkien posthumous book presents the creation of Arda and the history of the First Age?

The Silmarillion presents the creation of Arda and the history of the First Age.

The Silmarillion was edited by Christopher Tolkien and published in 1977, four years after J.R.R. Tolkien’s death. It brings together narratives about the creation of the world, the Ainur, the Valar, the Elves, and the long conflicts involving Morgoth and the Silmarils.

The book is not a conventional novel. It contains several connected sections, including the Ainulindalë, Valaquenta, Quenta Silmarillion, Akallabêth, and Of the Rings of Power and the Third Age. Together, they provide a mythic history behind the later stories of Middle-earth.

Because Tolkien revised these materials repeatedly, Christopher had to make editorial choices when preparing the volume. The published book is therefore a carefully assembled presentation of Tolkien’s mythology, not a final manuscript arranged by Tolkien himself.