Galactic empires are a science fiction setting trope, in which most or all of the habitable planets in the setting's galaxy are ruled by a single centralized political entity. Galactic empires most frequently appear in works in the sub-genres of science fantasy and space opera, although they may appear in other sub-genres as well. Works featuring galactic empires may have them as the story's focus, chronicling the empire's growth and/or decline. Alternatively, they may merely serve as a backdrop against which the events of the story play out.

Space opera is a subgenre of science fiction that emphasizes space warfare, with use of melodramatic, risk-taking space adventures, relationships, and chivalric romance. Set mainly or entirely in outer space, it features technological and social advancements in faster-than-light travel, futuristic weapons, and sophisticated technology, on a backdrop of galactic empires and interstellar wars with fictional aliens, often in fictional galaxies. The term does not refer to opera music, but instead originally referred to the melodrama, scope, and formulaicness of operas, much as used in "horse opera", a 1930s phrase for a clichéd and formulaic Western film, and "soap opera", a melodramatic television series. Space operas emerged in the 1930s and continue to be produced in literature, film, comics, television, video games and board games.