Serpent's Reach is a 1980 science fiction novel by the United States science fiction and fantasy author C. J. Cherryh. The book was nominated for the Locus Award for Best Novel in 1981 and is set in the author's Alliance-Union universe.
The book is set in the constellation Hydrus, which is known in the Alliance-Union universe as the "Hydri Reach", and also as "Serpent's Reach", from which the book takes its title. The Hydri stars are home to the alien Majat, an insectoid race with a hive-mind consciousness.
The entire constellation is under strict quarantine due to the dangers inherent in human-Majat interaction. The first contact with the Majat, for example, resulted in the human delegation being eaten. Humans do live in the Hydri stars, however, because Union had established colonies there before ceding Serpent's Reach to the Alliance, which subsequently imposed the quarantine. A space station orbiting the planet Beta Hydri II?, called Istra, serves as the sole point of contact between the Alliance and the human/Majat society of the Hydri stars.