Which Tolkien book was published posthumously in 1980 from unfinished Middle-earth writings?

Unfinished Tales was published posthumously in 1980 from J.R.R. Tolkien’s unfinished Middle-earth writings. Christopher Tolkien edited the collection and supplied explanatory notes for its varied texts.

The book gathers narratives and fragments from different periods of Tolkien’s writing. Its subjects include events in the First, Second, and Third Ages, along with material related to Númenor, the Istari, Gondor, Rohan, and the history of the Ring. Some sections are relatively complete stories, while others preserve drafts or alternative versions.

Unfinished Tales is not a conventional single novel and should not be confused with The Silmarillion, which was published in 1977. The collection is valuable because it expands or complicates details that receive only brief treatment in The Lord of the Rings. Christopher Tolkien’s editorial commentary helps readers understand where the texts fit within the development of his father’s mythology.