Despite the thousands of reports of unidentified flying objects made yearly around the world, there are a few commonalties in the sightings. Regardless of shape, many UFO's give off their own luminescence. This is thought to be caused by ionization of the air surrounding the surface or possibly vents on the craft. It is believed to work similarly to what occurs inside a neon light tube. This is usually of an orangish or yellow color when seen at night. It also explains the hazy, wavering appearance of UFO's during daylight.

By far the most common shape of a UFO is the ubiquitous "saucer" or "disk" shape. Often the craft will appear to have a flat bottom or a slightly convex hollow. These are the one's described as "hubcaps". Occasionally there will be a more pronounced upper hemispherical shape. A type of dome or "transparent cockpit" shape is reported on the top of the round, spinning craft. These "classic" flying saucers are the usual model for cartoons containing "little green men".

Other saucers show a less detailed shape. Many reports come in about the lenticular saucers that appear to be two shallow bowls glued together at the rim. They are usually dark, greyish to black and, like the 2006 O'Hara Airport sighting in Chicago, USA, can be described "like an M&M candy".

The "straw hat" flying saucers are generally described as being like a coin with a rim. Rising above this edge is usually a secondary superstructure that gives them their distinctly hat-like appearance. They have occasionally been reported as looking like two hats glued together at the rim. The bottom and top of these craft are generally very noticeably flat.

Falling into this category is also the anomalous "mushroom" shaped UFO's like the alleged "Gulf Breeze, Florida saucer. The bell-shaped saucers also fit here along with the ones that have been described as "an upside down coffee cup in a saucer".

These are generally the most maneuverable of all the unknown flying objects. They seem to be able to defy not only gravity but motion, speed and inertial forces as well. While they are known to hover quite well, they also are known for such amazing maneuverability as to rip a conventional craft to bits. They are usually described as rotating or spinning along their horizontal axis when seen close enough to detect the motion. On can only assume it is merely the outer rim that spins while the central core containing possible pilot and crew remains stable.