The Tolkien book published posthumously in 1977 as a history of Middle-earth’s earliest ages was The Silmarillion.
The volume was assembled by Christopher Tolkien from manuscripts his father had developed and revised over many decades. It begins with the creation of Eä and continues through the histories of the Ainur, the Elves, and the struggles of the First Age.
Its central narratives include the rebellion of the Noldor, the wars against Morgoth, and the stories of Beren and Lúthien, Túrin Turambar, and the fall of Gondolin. These tales provide the deep background later referenced in The Hobbit and The Lord of the Rings.
The title can cause confusion because The Silmarillion is both a book and the name associated with the three jewels at its center. It is also distinct from Unfinished Tales, another posthumous collection published in 1980.