What is the title of J.R.R. Tolkien’s posthumously published mythology of the First Age?

J.R.R. Tolkien’s posthumously published mythology of the First Age is The Silmarillion.

The Silmarillion was edited and published by Christopher Tolkien in 1977, four years after his father’s death. It presents the creation of Tolkien’s world, the history of the Valar, the awakening of the Elves, and the wars surrounding the Silmarils. Much of the book takes place in the First Age, long before The Hobbit and The Lord of the Rings.

The title refers to the three Silmarils, jewels made by Fëanor that contain the light of the Two Trees of Valinor. Their theft by Morgoth drives much of the book’s central conflict. The volume also includes stories involving Beren and Lúthien, Túrin Turambar, and Eärendil.

It is not a conventional single novel. Christopher Tolkien assembled material from drafts, revisions, annals, and related texts. That editorial history explains differences in style and detail across its sections.