The History of Middle-earth
The first five books discuss about the ancient history of The Silmarillion and relational texts. From the sixth to the ninth, the books discuss about the history of Númenor in the formation of The Notion Club Papers. The books ten and eleven back to the Silmarillion, with the Annals of Beleriand and the Annals of Aman. The twelfth book discuss about the creation of Lord of the Rings' appendix.