Nemesis is a science fiction novel by Isaac Asimov. It was one of his later science fiction novels; it was published in 1989, only three years before his death. The novel is only loosely related to the future history into which he attempted to integrate his science fiction output.

The novel is set in an era in which interstellar travel is in the process of being discovered and perfected. The demands of the plot required Asimov to hypothesise a planetary system about a star named Nemesis. At the time of the writing, this name was given to a theoretical companion to our sun which could provide a mechanism for periodic disturbances of comets in the Oort cloud, which would then fall inwards causing mass extinctions. The red dwarf star in the book turns out to not be this companion, simply passing through the solar system.

Interestingly, the resulting planetary system in the book included a Jovian planet in a very short period orbit about its primary star. This was a radical idea in 1989, but was vindicated with the discovery of the first extrasolar planet orbiting a sun-like star (that orbiting 51 Pegasi) in 1995.