Which Tolkien work was published posthumously in 1980 as an account of Númenor and Middle-earth?

Unfinished Tales was published posthumously in 1980 as a collection of narratives from Númenor and Middle-earth. Christopher Tolkien edited the material from his father’s papers and supplied extensive editorial commentary.

The book contains stories and fragments that expand the history of the First, Second, and Third Ages. Its subjects include Númenor, the origins of the Istari, Galadriel and Celeborn, and the journeys of the Rohirrim. Some pieces are relatively complete, while others survive in alternate versions or unfinished forms.

Unfinished Tales is often confused with The History of Middle-earth, a twelve-volume series that Christopher Tolkien published between 1983 and 1996. It is also distinct from The Silmarillion, which appeared in 1977 as a shaped presentation of Tolkien’s mythology. Because the texts in Unfinished Tales vary in completeness, the book is especially valuable for showing Tolkien’s revisions and unresolved ideas.