The Book of the Long Sun (1993–1996) is a series of four science fantasy novels or one four-volume novel by the American author Gene Wolfe. It is set in the same universe as The Book of the New Sun series that Wolfe inaugurated in 1980, and the Internet Science Fiction Database catalogs them both as sub-series of the "Solar Cycle", along with other writings. The Long Sun story is continued in The Book of the Short Sun (1999–2001), a series of three novels or one in three volumes. In Short Sun the relation to the original New Sun is made clear.