Which Tolkien novel was published posthumously in 1977, four years after his death?

The Silmarillion was published posthumously in 1977, four years after J.R.R. Tolkien’s death.

Tolkien had worked on the legends that became The Silmarillion for much of his life, but he did not complete a final publishable form. The book was edited and organized by his son Christopher Tolkien, who assembled material from manuscripts spanning different periods of Tolkien’s writing. It appeared on 15 September 1977.

The work presents the mythology and history behind Middle-earth, beginning with the creation of the world and continuing through the First Age and later events. Its major sections include the Ainulindalë, the Valaquenta, the Quenta Silmarillion, the Akallabêth, and “Of the Rings of Power and the Third Age.”

The Silmarillion is sometimes mistaken for a straightforward sequel to The Lord of the Rings. It is instead a collection of mythic histories, genealogies, and legends written in varied styles. Its posthumous editorial history explains why it differs in form from Tolkien’s published novels.