What is the title of Tolkien’s posthumously published collection of First Age myths?

The Silmarillion is Tolkien’s posthumously published collection of First Age myths.

Christopher Tolkien edited the work and published it in 1977, four years after his father’s death. It presents the creation of Tolkien’s world, the angelic beings called the Valar, the making of the Silmarils, and the wars against Morgoth. Its scope reaches from the beginning of Arda to the end of the First Age.

Unlike The Hobbit and The Lord of the Rings, The Silmarillion is not a single continuous novel with one central protagonist. It is a collection of linked mythological narratives, histories, genealogies, and legends. The title comes from the Silmarils, three jewels made by Fëanor. Unfinished Tales and The Children of Húrin are related Tolkien works, but neither is the main published collection of these First Age myths.