Passport to Magonia: From Folklore to Flying Saucers

Passport to Magonia (Regnery, 1969) is the book in which Jacques Vallée broke with the idea that UFOs are simply spacecraft from other planets. Comparing modern close encounters with centuries of folklore, from fairies and elves to the medieval legend of Magonia, a land in the clouds, and to religious apparitions, he argued that the same phenomenon, or the same human response to it, appears in each era in the dress of its time. A long appendix catalogues landing reports from the previous century.

It became one of the founding texts of what is often called the interdimensional or "control system" view of UFOs, and led some American ufologists to treat Vallée as an outsider. Sceptics read the same parallels the other way: as evidence that UFO encounters are a modern form of folklore with psychological and cultural roots.

Sources: Wikipedia