Which Tolkien work was published posthumously in 1977 after editing by Christopher Tolkien?

The Silmarillion was published posthumously in 1977 after editing by Christopher Tolkien.

J.R.R. Tolkien died in 1973, leaving a large and complex body of mythology in different versions and stages of completion. Christopher Tolkien edited these materials into a publishable volume, with assistance from the writer Guy Gavriel Kay, and The Silmarillion appeared on 15 September 1977.

The book presents the creation of Eä, the history of the Valar and Elves, and major events of the First Age. It includes the Valaquenta, the Quenta Silmarillion, the Akallabêth, and the “Of the Rings of Power and the Third Age” section.

Unfinished Tales and The Children of Húrin were also edited and published after Tolkien’s death, but they appeared later. The Silmarillion is the major 1977 posthumous volume most directly associated with Christopher Tolkien’s editorial work.