In political science, a reactionary or a reactionist is a person who holds political views that favor a return to the status quo ante—the previous political state of society—which the person believes possessed positive characteristics that are absent from contemporary society. As a descriptor term, reactionary derives from the ideological context of the left–right political spectrum. As an adjective, the word reactionary describes points of view and policies meant to restore a status quo ante.

The left–right political spectrum is a system of classifying political positions, ideologies and parties, with emphasis placed upon issues of social equality and social hierarchy. In addition to positions on the left and on the right, there are centrist and moderate positions, which are not strongly aligned with either end of the spectrum. It originated during the French Revolution based on the seating in the French National Assembly.