What is the name of the fictional manuscript Tolkien used as the frame for The Lord of the Rings?

The fictional manuscript framing The Lord of the Rings is The Red Book of Westmarch.

Within Tolkien’s imagined history, the Red Book is a collection of writings associated first with Bilbo Baggins and later with Frodo and Samwise Gamgee. It is presented as a source for the account of the War of the Ring, including Bilbo’s narrative and Frodo’s record of the journey to destroy the One Ring.

The name comes from its red binding and its association with the Westmarch, a region later granted to the Shire. Tolkien used the manuscript conceit to make the epic feel like a translated historical record rather than a story told without an internal source. Characters such as Meriadoc Brandybuck and other scholars are connected with preserving or expanding the material.

The Red Book is different from the Book of Mazarbul, a record found in the Mines of Moria, and from various “Annals” concerning earlier ages. Those are separate fictional texts within Tolkien’s wider literary history, not the principal frame for The Lord of the Rings.