Which Tolkien manuscript did Christopher Tolkien publish in 1977?

Christopher Tolkien published The Silmarillion in 1977 from his father’s extensive posthumous writings.

J.R.R. Tolkien had worked on the mythology behind the book for decades, but he did not complete a final version suitable for publication during his lifetime. Christopher edited and arranged drafts, notes, and differing versions into a single volume covering the creation of the world, the Elder Days, and later ages.

The Silmarillion is not a conventional sequel to The Lord of the Rings. It is a collection of mythic histories and related texts, including the creation story and narratives about the great jewels called the Silmarils. Its publication helped readers understand the deep background behind Tolkien’s later novels.