The posthumous 1977 book edited by Christopher Tolkien from J.R.R. Tolkien’s writings is The Silmarillion.
The Silmarillion was published on 15 September 1977, four years after Tolkien’s death. Christopher Tolkien edited and arranged a large body of unfinished and variant material to present a connected account of the history, legends, and peoples of Tolkien’s imagined world.
The book begins with the creation of the world in the Ainulindalë and continues through the history of Valinor, the First Age, and later events. Major narratives include the creation of the Silmarils, the rebellion of Fëanor, the wars against Morgoth, and the stories of Beren and Lúthien and Túrin Turambar.
Unlike The Lord of the Rings, The Silmarillion was not finalized by J.R.R. Tolkien as a single completed manuscript. Its editorial history explains differences in style and detail between sections. Unfinished Tales and The History of Middle-earth are separate posthumous publications, not alternate names for this book.