At the end of the 1937 J.R.R. Tolkien reluctantly set aside his now greatly elaborated work on the myths and heroic legends of Valinor and Middle-earth and began The Lord of the Rings. This fifth volume of The History of Middle-earth, edited by Christopher Tolkien, completes the presentation of the whole compass of his writing on those themes up to that time. Later forms of the Annuals of Valinor and the Annals of Berleriand had been composed, The Silmarillion was nearing completion in a greatly amplified version, and a new map had been made; the myth of the Music of the Ainur had become a separate work; and the legend of the Downfall of Numenor had already entered in a primitive form, introducing the cardinal ideas of the World Made Round and the Straight Path into the vanished West.

Closely associated with this was the abandoned time-travel story, The Lost Road, which was to link the world of Numenor and Middle-earth with the legends of many other times and peoples.

A long essay, The Lhammas, had been written on the ever more complex relations of the languages and dialects of Middle-earth; and an etymological dictionary had been undertaken, in which a great number of words and names in the Elvish languages were registered and their formation explained - thus providing by far the most extensive account of their vocabularies that has appeared.