The Book of the New Sun is the name of the manuscript written by Severian. It was translated into English by Gene Wolfe and published under the same name.

In his later years as Autarch, Severian wrote down the story of his rise to the office, starting from his adolescence in the Guild of the Torturers. He finished his account before departing for Yesod to bring the New Sun, and put the book in Ultan's library in the Citadel.

While en route to Yesod on Tzadkiel's ship, Severian produced a verbatim copy of this manuscript, aided by his eidetic memory. He flung this second copy out into space, where it presumably eventually ended up on our Earth in the hands of Gene Wolfe, who translated and published it.