Which Tolkien work was published posthumously in 1980 as a collection of Middle-earth texts?

Unfinished Tales was published posthumously in 1980 as a collection of Middle-earth texts.

Christopher Tolkien edited and assembled the volume from incomplete or variant writings by his father. The book expands stories from several periods of Middle-earth’s history, including the First Age, the Second Age, and the Third Age.

Its contents include material about Tuor, Númenor, the history of Galadriel and Celeborn, the disaster of the Gladden Fields, and the coming of the Rohirrim. Christopher’s editorial notes explain differences between versions and identify places where Tolkien had not completed or harmonized the narratives.

The title is descriptive: these are not simply deleted chapters from The Lord of the Rings, and many sections were never intended as a finished single work. The volume followed The Silmarillion, published in 1977, and preceded Christopher Tolkien’s later multi-volume History of Middle-earth.