The title refers to a legendary land in the clouds described in medieval French chronicles where "aerial people" were said to dwell.

The first half builds Vallée's theoretical case, moving between medieval theology, psychology, and folklore to demonstrate that modern "aliens" are the same entities once called gods, angels, or monsters.

He compares modern alien abductions to medieval tales of being taken to Fairyland. Elements like "missing time," strange food offerings (e.g., barley cakes ), and medical examinations are shown to have near-identical counterparts in ancient myths of elves, demons, and gnomes.

The book famously includes a massive appendix—"A Century of UFO Landings"—cataloging roughly 900 cases of alleged landings and occupants recorded between 1868 and 1968. Review: Passport to Magonia (1969) by Jacques Vallée

The book's central premise is that modern UFO encounters are part of a persistent phenomenon that has been with humanity throughout history, appearing in different forms depending on the cultural and technological context of the time. Vallée draws striking parallels between contemporary reports and historical folklore:

Vallée argues that the phenomenon adapts its appearance—from "celestial chariots" in the Bible to high-tech "flying saucers" today—as a way to interact with the collective human unconscious. Structure and Content