In the fiction, it is a collection of writings in which the events of The Hobbit and The Lord of the Rings were recounted by their characters, and from which Tolkien supposedly derived these and other works.
In reality, Tolkien modelled its name on the Red Book of Hergest, and followed a tradition in English literature established by Samuel Richardson in the 18th century.
He was also attempting, according to the scholar Gergely Nagy, to fit The Lord of the Rings into his presentation of his legendarium as a genuine-seeming collection of tales and myths, by ascribing the documents to the hobbit Bilbo Baggins.
[T 2] Bilbo expands his memoirs into a record of the events of The Lord of the Rings, including the exploits of his kinsman Frodo Baggins and others.
At the close of Tolkien's main narrative, the work is almost complete, and Frodo leaves the task to his gardener Samwise Gamgee.
[T 1] Tolkien states that the original Red Book of Westmarch was not preserved, but that several copies, with various notes and later additions, were made.
[T 1] The story then runs that a copy of a revised and expanded Thain's Book was made probably by request of Peregrin's great-grandson and delivered to the Shire.
Tolkien mentions several other supposedly historical documents related to the Red Book, but it is unclear whether these were integrated into editions.
These works include the Tale of Years (part of which was used as the timeline for The Lord of the Rings) and Herblore of the Shire, supposedly written by Frodo's contemporary Meriadoc Brandybuck, used for information about pipe-weed.
Frodo looks upon the going "there and back again" as an ideal throughout The Lord of the Rings similar to the Greek concept of νόστος (nostos, a heroic return).
[6] The "found manuscript conceit",[1] employed by Tolkien to situate The Hobbit as a part of The Red Book of Westmarch, has been used in English literature since Samuel Richardson's novels Pamela; or, Virtue Rewarded (1740) and Clarissa; or, The History of a Young Lady (1747–1748); Tolkien used it also in his incomplete time travel novel, The Notion Club Papers.
[1][7] Gergely Nagy notes that Tolkien wanted to present the complex set of writings of his legendarium as a seemingly-genuine collection of tales and myths within the frame of his fictional Middle-earth; he modified The Lord of the Rings to ascribe the documents to Bilbo, supposedly written in the years he spent in Rivendell, and preserved in the fictitious Red Book of Westmarch.
The exchange is tweaked to symbolize Bilbo's unburdening from the great weight of the ring; this frees him to choose his own story's ending.
[11] In 1974, Houghton Mifflin Harcourt published a one-volume edition of The Lord of the Rings, bound in red imitation leather.