Which Tolkien novel was published posthumously in 1977 as a collection of Middle-earth myths?

The Silmarillion was published posthumously in 1977 as a collection of J.R.R. Tolkien’s Middle-earth myths.

The volume was assembled from writings that Tolkien had developed and revised across much of his life. It begins with a creation account and continues through the histories of Valinor, the Elves, the First Age and the great conflicts involving Morgoth. Its title refers especially to the three Silmarils, jewels made by Fëanor that drive much of the central tragedy.

Christopher Tolkien edited the material after his father’s death, since Tolkien had not produced a final, unified manuscript suitable for publication. This editorial history distinguishes The Silmarillion from Tolkien’s completed novels.

Unfinished Tales and The Children of Húrin were also published after Tolkien’s death, but they are different kinds of books. The first is a collection of narratives and notes, while the second is an expanded presentation of one First Age story. The Silmarillion is the work that most broadly presents Tolkien’s mythology.