Several outlets have published lists ranking the greatest sci-fi movies, with some focusing on specific time periods, such as before 2001 or since 2010, and others considering the last 75 or 100 years. The lists vary in their scope and criteria, with some highlighting masterpieces, characters, or thriller and space-themed films. It appears that there is no single, unified ranking of the greatest sci-fi movies, as different outlets have compiled distinct lists with different parameters.