The Phoenix Lights was a mass UFO sighting which occurred in Phoenix, Arizona, and Sonora, Mexico on Thursday, March 13, 1997.

Lights of varying descriptions were reported by thousands of people between 19:30 and 22:30 MST, in a space of about 300 miles (480 km), from the Nevada line, through Phoenix, to the edge of Tucson.

There were allegedly two distinct events involved in the incident: a triangular formation of lights seen to pass over the state, and a series of stationary lights seen in the Phoenix area. The United States Air Force later identified the second group of lights as flares dropped by A-10 Warthog aircraft that were on training exercises at the Barry Goldwater Range in southwest Arizona.

Witnesses claim to have observed a huge V-shaped (several football field sized), coherently-moving dark UFO (stars would disappear behind the object and reappear as it passed by), producing no sound, and containing five spherical lights or possibly light-emitting engines. Fife Symington, the governor at the time, was one witness to this incident. As governor he ridiculed the idea of alien origin, but several years later he called the lights he saw "otherworldly" after admitting he saw a similar UFO.

The first event — the "V", which appeared over northern Arizona and gradually traveled south over nearly the entire length of the state, eventually passing south of Tucson — was the apparently "wedge-shaped" object reported by then-Governor Symington and many others. This event started at about 20:15 MST over the Prescott area, and was seen south of Tucson by about 20:45 MST.

Proponents of two separate events propose that the first event still has no provable explanation, but that some evidence exists that the lights were in fact airplanes. According to an article by reporter Janet Gonzales that appeared in the Phoenix New Times, videotape of the v shape shows the lights moving as separate entities, not as a single object; a phenomenon known as illusory contours can cause the human eye to see unconnected lines or dots as forming a single shape.

Mitch Stanley, an amateur astronomer, observed high altitude lights flying in formation using a Dobsonian telescope giving 43× magnification. After observing the lights, he told his mother, who was present at the time, that the lights were aircraft. According to Stanley, the lights were quite clearly individual airplanes; a companion who was with him recalled asking Stanley at the time what the lights were, and he said, "Planes". When Stanley first gave an account of his observation at the Discovery Channel Town Hall Meeting with all the witnesses there he was shouted down in his assertion that what he saw was what other witnesses saw. Some have claimed that Stanley was seeing Maryland Air National Guard jets flying in formation during a routine training mission at the Barry M. Goldwater Air Force Range south of Phoenix

The second event was the set of nine lights appearing to "hover" over the city of Phoenix at around 10 pm (22:00 MST). The second event has been more thoroughly covered by the media, due in part to the numerous video images taken of the lights. This was also observed by numerous people who might have thought they were seeing the same lights as those reported earlier.

The U.S. Air Force explained the second event as slow-falling, long-burning LUU-2B/B illumination flares dropped by a flight of four A-10 Warthog aircraft on a training exercise at the Barry Goldwater Range at Luke Air Force Base. According to this explanation, the flares would have been visible in Phoenix, and they would have appeared to hover due to rising heat from the burning flares creating a "balloon" effect on their parachutes, slowing the descent. The lights then appeared to wink out as they fell behind the Sierra Estrella, a mountain range to the southwest of Phoenix.

There was minimal news coverage at the time of the incident. In Phoenix, a small number of local news outlets noted the event, but it received little attention beyond that. But on June 18, 1997, USA Today ran a front-page story that brought national attention to the case. This was followed by news coverage on the ABC and NBC television networks. The case quickly caught the popular imagination and has since become a staple of UFO-related documentary television, including specials produced by the History Channel and the Discovery Channel

Shortly after the lights, Arizona Governor Fife Symington III held a press conference, stating that "they found who was responsible". He proceeded to make light of the situation by bringing his aide on stage dressed in an alien costume. (Dateline, NBC). But in March 2007, Symington said that he had witnessed one of the "crafts of unknown origin" during the 1997 event, although he did not go public with the information. In an interview with The Daily Courier in Prescott, Arizona, Symington said, "I'm a pilot and I know just about every machine that flies. It was bigger than anything that I've ever seen. It remains a great mystery. Other people saw it, responsible people. I don't know why people would ridicule it". Symington had earlier said, "It was enormous and inexplicable. Who knows where it came from? A lot of people saw it, and I saw it too. It was dramatic. And it couldn't have been flares because it was too symmetrical. It had a geometric outline, a constant shape."