The Book of Lost Tales 1 stands at the beginning of the entire conception of Middle-earth and Valinor. Embedded in English legend and English association, they were set in the narrative frame of a great westward voyage over the Ocean by a mariner named Eriol (or Ælfwine) to Tol Eressëa, the Lonely Isle, where Elves dwelt. From them, he learned their true story, the Lost Tales of Elfinesse.

In the Tales are found the earliest accounts and original ideas of Gods and Elves; Dwarves and Orcs; the Silmarils and the Two Trees of Valinor; Nargothrond and Gondolin; and the geography and cosmology of the invented world.