The title of Tolkien’s posthumously published collection of First Age legends edited by Christopher Tolkien is The Silmarillion.
The Silmarillion was published in 1977, four years after J.R.R. Tolkien’s death. Christopher Tolkien edited and organized material that his father had developed, revised, and expanded over many decades. The book presents the mythology and history behind the later narratives of Middle-earth.
Its central section, the Quenta Silmarillion, recounts the creation of the Silmarils by Fëanor and the wars that followed their theft by Morgoth. The volume also includes the Ainulindalë, the Valaquenta, and the Akallabêth, along with material about the Third Age.
Because Tolkien left the manuscripts in different stages and versions, The Silmarillion is an editorial reconstruction rather than a single finished manuscript prepared for publication by Tolkien himself. Christopher Tolkien’s editorial work made the collection available as a coherent book.