Little green men is the stereotypical portrayal of extraterrestrials as little humanoid 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 greys, whose skin color is described as not green, but grey.

During the reports of flying saucers in the 1950s, the term "little green men" came into popular usage in reference to aliens. In one classic case, the Kelly-Hopkinsville sighting in 1955, two rural Kentucky men described a supposed encounter with metallic-silver, somewhat humanoid-looking aliens no more than 4 feet (1.2 m) in height. Employing journalistic licence and deviating from the witnesses' accounts, The Evansville Courier used the term "little green men" in writing up the story. Other media then followed suit.