What is the title of J.R.R. Tolkien’s posthumously published Middle-earth mythology collection?

J.R.R. Tolkien’s posthumously published Middle-earth mythology collection is The Silmarillion.

The Silmarillion was published in 1977, four years after Tolkien’s death. His son Christopher Tolkien edited and arranged the material, with assistance from the author Guy Gavriel Kay. The book presents mythic and historical narratives concerning the creation of the world, the Ainur, the First Age, and the great conflicts surrounding the Silmarils.

Unlike The Hobbit and The Lord of the Rings, The Silmarillion was not a finished single novel prepared for publication by Tolkien. It developed from writings created and revised across much of his life. This explains differences in style, structure, and versions of events within the collection.

The title refers especially to the three Silmarils, jewels made by Fëanor. The book is broader than their immediate story, covering the cosmology and history that provide the deep background of Tolkien’s best-known novels.