After someone has had an encounter with an Unidentified Flying Object, they are sometimes visited by one or more men claiming to represent an official government body such as the Air Force. They frequently dress in black suits, wear sunglasses, and have odd tech on their person (like unexplained wires up their sleeves). They may drive older model cars that appear to be brand new. They act in an unnatural manner, ask odd and sometimes deeply personal questions and make irrelevant remarks. Their visit usually winds up with a threat of some unspecified reprisal if the contactee goes public with his or her story.

Tales of these encounters date back to antiquity; some folklorists have pointed out the similarities between MIB and stories of meetings with the Devil, identified as "The Black Man". Residents of a medieval village suffering a plague reported a visit by several individuals dressed in black and carrying "scythes" with which they spread sickness (biological warfare?). Perhaps the most famous modern appearance of MIB was in West Virginia in the late 1960s, in the wake of the Mothman sightings.

Jesse Ventura and Alex Trebek did an excellent job of portraying a pair of Men In Black as they are commonly described in the X-Files episode "Jose Chung's From Outer Space".