Hard science fiction is a category of science fiction characterized by an emphasis on scientific or technical detail, or on scientific accuracy, or on both. The term was first used in print in 1957 by P. Schuyler Miller in a review of John W. Campbell, Jr.'s Islands of Space in Astounding Science Fiction. The complementary term soft science fiction (formed by analogy to "hard science fiction") first appeared in the late 1970s. The term is formed by analogy to the popular distinction between the "hard" (natural) and "soft" (social) sciences. The science fiction critic Gary Westfahl argues that neither term is part of a rigorous taxonomy—instead they are approximate ways of characterizing stories that reviewers and commentators have found useful.

Today, the term "soft science fiction" is often used to refer to science fiction stories which lack a scientific focus or rigorous adherence to known science. The categorization "hard science fiction" represents a position on a broad continuum--ranging from "softer" to "harder".