Space travel. Time travel. Aliens. Parallel worlds. Dystopian futures. Explorations of the interface between humanity and AI…. Science fiction is one of the most far-ranging narrative genres in existence.

What is science fiction? One of sci-fi’s most prolific and respected authors, Isaac Asimov, defined it as “that branch of literature which deals with the reaction of human beings to changes in science and technology.” Another giant in the field, Robert A. Heinlein, called it “realistic speculation about possible future events, based solidly on adequate knowledge of the real world.” (These are the 23 best sci-fi movies about time travel.)  

Sci-fi films are nearly as old as science fiction itself. One of the earliest movies ever made was “A Trip to the Moon,” a silent short made in 1902 by French filmmaker Georges Méliès. The same director’s three-minute short “The House of the Devil,” from 1896, is considered to have been the first horror film — a related genre. 

The first feature length sci-fi movie was German director Fritz Lang’s 1927 “Metropolis,” now considered one of the greatest and most influential films of all time. Countless cinematic works of science fiction, horror, and fantasy have followed. (Check out the best sci-fi movie the year you were born.)

To determine the best sci-fi movies of all time, 24/7 Tempo developed an index using average ratings on IMDb, an online movie database owned by Amazon, and a combination of audience scores and Tomatometer scores on Rotten Tomatoes, an online movie and TV review aggregator, as of October 2021. All ratings were weighted equally. Only movies with at least 15,000 audience votes on either IMDb or Rotten Tomatoes were considered. The countless “Star Wars” movies and superhero fantasies based on Marvel Comics or DC Comics characters were excluded from consideration. Directorial credits and cast information comes from IMDb.

Click here to see the 50 best sci-fi movies of all time

Great sci-fi doesn’t just entertain. It criticizes the present and warns us (or excites us) about the future. It makes us think. It provides us with a sense of wonder. But, yeah, it can be pretty darn entertaining, too.