The Book of the New Sun (1980–1983, 1987) is a four-volume science fantasy novel written by the American author Gene Wolfe. The work is in four parts with a fifth novel acting as a coda to the main story. It inaugurated the "Solar Cycle" that Wolfe continued by setting other works in the same universe (The Book of the Long Sun series, and The Book of the Short Sun series).

It chronicles the journey of Severian, a journeyman torturer from the Order of the Seekers for Truth and Penitence. After helping a client kill herself, he is exiled in disgrace to journey to the distant city of Thrax where he is to live out his days as their executioner. Severian lives in the ancient city of Nessus in a nation called the Commonwealth, ruled by the Autarch, in the Southern Hemisphere. It is at war with Ascia, its totalitarian northern neighbor. It is a first-person narrative, ostensibly translated by Wolfe into contemporary English, set in a distant future when the Sun has dimmed and Earth is cooler (a "Dying Earth" story).

The four volumes and additional fifth coda are:

In a 1998 poll of its subscribers, Locus magazine ranked the tetralogy number three among 36 all-time best fantasy novels before 1990.