This is a list of notable reported sightings of unidentified flying objects (UFOs) arranged by date. It includes reports of close encounters and abductions. This list is not an endorsement of the extraterrestrial hypothesis, the psychosocial hypothesis, the interdimensional hypothesis, the field of ufology in general, or UFO religions.

The term UFO was coined by officer Edward J. Ruppelt who investigated aerial phenomena for the United States Air Force in his role as leader of Project Blue Book during the 1950s. Before Project Blue Book, UFOs were often referred to as "flying saucers" in reference to the widely publicized Kenneth Arnold UFO sighting. Ruppelt explained that "the term 'flying saucer' is misleading when applied to objects of every conceivable shape and performance".

What would later be called UFOs were reported before the 1947 flying saucer craze. Allied pilots during World War II described them as foo fighters. In Sweden, early 20th-century UFOs were called Spökraketer or ghost rockets. Mystery airships reported in the late 19th century, are seen as predecessors to UFO sightings. Unexplained aerial phenomena have been recorded stretching back into antiquity. Prior to the Scientific Revolution, they were often interpreted through the lenses of gods, ghosts, demons, and omens. Rice University professor of religion Jeffrey J. Kripal says of UFO encounters, "These are not especially rare events, nor are they restricted to any culture, race, religion, or time period."