The letters are accompanied by detailed notes, and by an index compiled by the Tolkien scholars Christina Scull and Wayne G. Hammond.

I mean the terrible recurrent dream (beginning with memory) of the Great Wave, towering up, and coming in ineluctably over the trees and green fields.

In 1951, Tolkien hoped that Collins would publish both The Lord of the Rings and a selection from his legendarium, including material that his son Christopher later edited to form The Silmarillion.

To help persuade them that the two were "interdependent and indivisible",[5] Tolkien sent a long letter (#131) to Milton Waldman of Collins, outlining the foundations and ambitions of his writings, and giving a potted history of the whole story from the creation, through the First, Second and Third Ages, and finishing with a reference to The Hobbit and a lengthy outline of The Lord of the Rings.

[8] Other letters discuss subjects as widely varied as the location of Middle-earth ("the actual Old World of this planet", p.220, #165), the shape of hobbits' ears ("only slightly pointed", #27) and the source of the "Downfall of Númenor" in Tolkien's recurring dream of Atlantis (#163).

[13] Hannu Hiilos, reviewing the book, echoes the editor's remark that the letters had been chosen from "a very large volume of material".

In addition, he writes, Tolkien's views, coloured by his position on religion, morals, and politics, come across clearly in his wartime letters to Christopher.

[16] The Tolkien Collector's Guide notes that the 2023 edition is essentially the text that Carpenter prepared for Allen & Unwin in 1979, only to find that the publishers felt it was too long.

[18] Joseph Loconte in The Wall Street Journal writes that the new edition offers "some revealing gems", but that "enthusiasts may be disappointed by what remains under lock and key.