There is a fairly substantial list of books that claim to document UFO sightings. In recent years, the alleged UFO crash in Roswell New Mexico in 1947 has tended to dominate popular discussions in this area, so I have listed several books that describe the Roswell incident. The other, recent, popular theme has been so-called alien abductions, but one can separate beliefs in UFOs and beliefs that people have been abducted by aliens and returned to earth. While beliefs in UFOs is certainly necessary for beliefs in alien abductions, the former does not entail the latter.
Berlitz, Charles & Moore, William. The Roswell Incident. Grosset & Dunlap, 1980. While the Roswell incident had been part of UFO lore for years, this book is largely responsible for making it the central exhibit in charges that the government has systematically covered up UFO landings and contact with extra-terrestrials.
Bernard, Raymond. The Hollow Earth: The Greatest Geographical Discovery in History. Bell, 1969. UFOs originate in the interior of the earth. Honest. Crank science and weird beliefs, but UFOs bring out the best and worst.
Clark, Jerome. The UFO Book: Encyclopedia of the Extraterrestrial. (*). Visible Ink, 1998. A lengthy treatment with entries for various UFO sightings and for people active on both sides of the issue. Valuable for listing of books, videos, and other resources.
Hopkins, Budd. Intruders: The Incredible Visitations at Copley Woods (*) Ballantine, 1987. An account of a reported alien abduction in Indianapolis. Missing Time: A Documented Study of UFO Abductions (Marek, 1981) by the same author has additional accounts. Hopkins is a leading advocate of the idea that aliens are here to stay and up to no good.
Hynek, J. Allen. The UFO Experience: A Scientific Inquiry. Ballantine, 1972. An older book by a person who wanted to approach UFOs as a legitimate area for scientific inquiry. A classic review of early alleged sightings.
Jacobs, David M. Secret Life: Firsthand Documented Accounts of UFO Abductions. (*). Simon & Schuster, 1992. Jacobs is an historian who along with John Mack, a psychiatrist at Harvard Medical School, is probably the leading and most persuasive advocate of UFO abductions. However, be warned that he presents incomplete information, and that many of the cases he presents are based on hypnotically-induced recall which is always suspect. In his later, The Threat: The Secret Agenda: What the Aliens Really Want ... And How They Plan to Get It (Simon & Schuster, 1998), Jacobs claims that aliens are not loveable anda re, in fact, rather nasty.
Klass, Philip J. UFO-Abductions: A Dangerous Game. Prometheus Books, 1989. A critical analysis of the many claims of abduction. The earlier UFOs: The Public Deceived (Prometheus Books, 1983) is critical of the evidence supporting UFOs generally.
Korff, Kal K. The Roswell UFO Crash: What They Don=t Want You To Know. Prometheus Books, 1997. Despite the fact that the author is less skeptical of UFO accounts than many others, he concludes there is no evidence of a UFO crash at Roswell.
Lewis, James (Ed.). The Gods Have Landed: New Religions from Other Worlds. SUNY Press, 1995. Papers dealing with the relationships of UFO encounters and religion with some emphasis on UFO cults such as Heaven's Gate.
Mack, John. Abduction: Human Encounters with Aliens. Ballantine Books, 1994. The Bible of the UFO abduction movement written by a Harvard psychiatrist who uses hypnotically induced recall to provide evidence for his ideas that aliens routinely abduct humans. Fascinating reading, but untrustworthy.
McAndrew, James and the Headquarters of the United States Air Force. The Roswell Report: Case Closed. The Government Printing Office, 1997. In 1947 a weather balloon landed near Roswell New Mexico, and after the publication of The Roswell Incident by William Moore and Charles Berlitz (1980) -- see above -- it has become a leading cause célèbre with charges of government coverups of genuine UFOs; more recently there has even been supposedly documented evidence of an autopsy of an alien found at the site of the Acrash@. The Air Force report is the last of a series of reports which explains the conflicting stories on the Roswell incident. This is definitive unless, of course, one believes that the government is systematically covering up a real incident.
Peebles, Curtis. Watch the Skies: A Chronicle of the Flying Saucer Myth. Smithsonian Institution Press, 1994. An recent criticism of reports of UFO sightings.
Randle, Kevin & Schmidt, Donald. UFO Crash at Roswell. Avon Books, 1991. One of the chief proponents of the idea of a UFO crash at Roswell and a subsequent government coverup. Also Randle & Schmidt, The Truth About the UFO Crash at Roswell (Avon, 1994).
Saler, Benson, Ziegler, Charles, & Moore, Charles UFO Crash at Roswell: The Genesis of a Modern Myth. Smithsonian Institution Press, 1997. An interesting attempt to explain the Roswell incident as a kind of folk myth or legend.
Sheaffer, Robert. The UFO Verdict: Examining the Evidence. Prometheus Books, 1986. A good but somewhat dated critique of the Roswell myth.