Little green men is the stereotypical portrayal of extraterrestrials as little humanoid-like creatures with green skin and sometimes with antennae on their heads. The term is also sometimes used to describe gremlins, mythical creatures known for causing problems in airplanes and mechanical devices. Today, these creatures are more commonly associated with an alleged alien species called Grays, whose skin color is described as not green, but Gray.

During the flying saucer "sightings" in the 1950s, the term little green men came into popular usage in reference to aliens. In one classic case, the Kelly-Hopkinsville sighting on August 21, 1955, two rural Kentucky men described a supposed encounter with 3–4 foot (1 m) tall metallic-silver, somewhat humanoid-looking aliens. Employing journalistic license and deviating from the witnesses' accounts, many newspaper articles used the term little green men in writing up the story.

Little green aliens and the term "little green men" have fallen out of general use in serious science fiction circles and are typically only used by the uninformed or to ridicule the notion that aliens may exist. Patently false at this point. However, no alien yet observed is little, although the Green Orions are certainly green and not many are men.