The Silmarillion was published posthumously in 1977 and presents the mythology of Middle-earth’s earliest ages. Christopher Tolkien edited the work from his father’s extensive manuscripts, with assistance from Guy Gavriel Kay.
The book opens with the creation of Eä through the Music of the Ainur and continues through the history of Arda. Its central narrative, the Quenta Silmarillion, concerns the Silmarils, the Noldorin exiles, and the wars against Morgoth in the First Age.
The published volume also includes the Valaquenta, a description of the Valar and Maiar; the Akallabêth, the account of Númenor; and Of the Rings of Power and the Third Age, which connects the mythology to the events of The Lord of the Rings.
The Silmarillion is not a conventional novel written in one continuous form. It is an editorially assembled collection of related texts, legends, annals, and narratives. Unfinished Tales and The Children of Húrin were also published after Tolkien’s death, but they are different volumes.