The Silmarillion was published posthumously in 1977 as a collection of Middle-earth creation myths.
The book opens with the Ainulindalë, a creation story describing the making of the world through music, and continues with accounts of the Valar, the Elves, and the great conflicts of the First Age. It also includes the Akallabêth, concerning the downfall of Númenor, and a section on the Rings of Power and the Third Age.
J.R.R. Tolkien worked on these stories for much of his life but did not complete a final version for publication. After his death, Christopher Tolkien edited material from many drafts into the form published in 1977. The result is more like a mythology or chronicle than a conventional novel.
Unfinished Tales appeared later, in 1980, and contains additional narratives and notes. The Children of Húrin was published in 2007 as a more unified edition of one tragic First Age story.