Which posthumously published book assembled J.R.R. Tolkien’s mythology of the First Age?

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

Christopher Tolkien edited and arranged The Silmarillion after his father’s death, and George Allen & Unwin published it in 1977. The book presents creation stories, the history of the Elves, the wars against Morgoth, and the tragedies of figures such as Túrin Turambar and Beren and Lúthien.

It is not a conventional single-volume novel. The work combines mythic narratives, annal-like material, genealogies, and linguistic history, reflecting Tolkien’s long process of revision. Unfinished Tales and The Children of Húrin also draw on Tolkien’s legendarium, but The Silmarillion is the central published compilation of the First Age mythology.