Jacques F. Vallée, Ph.D., (September 24, 1939) is a French-born venture capitalist, computer scientist, ufologist and former astronomer, currently residing in San Francisco, California in the United States. (He should not be confused with the Canadian astronomer Jacques P. Vallée.)

In mainstream science, Vallee is notable for co-developing the first computerized mapping of Mars for NASA, and for his work at SRI International in creating ARPANET, a precursor to the modern Internet. Vallee is also an important figure in the study of unidentified flying objects (UFOs), first noted for a defense of the scientific legitimacy of the extraterrestrial hypothesis and later for promoting the Interdimensional hypothesis.

In May 1955, Vallée first sighted an unidentified flying object over his Pontoise home. Six years later in 1961, while working on the staff of the French Space Committee, Vallée witnessed the destruction of the tracking tapes of unknown objects orbiting the earth. These events contributed to Vallée's long-standing interest in the UFO phenomenon.

In the mid-1960s, like many other UFO researchers, Vallée initially attempted to validate the popular Extraterrestrial Hypothesis (or ETH). Leading UFO researcher Jerome Clark^[4] argues that Vallée's first two UFO books were among the most scientifically sophisticated defenses of the ETH ever mounted.

However, by 1969, Vallée's conclusions had changed, and he publicly stated that the ETH was too narrow and ignored too much data. Vallée began exploring the commonalities between UFOs, cults,religious movements, angels, ghosts, cryptid sightings, and psychic phenomena. These links were first detailed in Vallee's third UFO book, Passport to Magonia: From Folklore to Flying Saucers.

As an alternative to the extraterrestrial visitation hypothesis, Vallée has suggested a multidimensional visitation hypothesis. This hypothesis represents an extension of the ETH where the alleged extraterrestrials could be potentially from anywhere. The entities could be multidimensional beyond space-time, and thus could coexist with humans, yet remain undetected.

Vallée's opposition to the popular ETH hypothesis was not well received by prominent U.S. ufologists, hence he was viewed as something of an outcast. Indeed, Vallée refers to himself as a "hereticamong heretics".

Vallée's opposition to the ETH theory is summarised in his paper, "Five Arguments Against the Extraterrestrial Origin of Unidentified Flying Objects," Journal of Scientific Exploration, 1990:

Scientific opinion has generally followed public opinion in the belief that unidentified flying objects either do not exist (the "natural phenomena hypothesis") or, if they do, must represent evidence of a visitation by some advanced race of space travellers (the extraterrestrial hypothesis or "ETH"). It is the view of the author that research on UFOs need not be restricted to these two alternatives. On the contrary, the accumulated data base exhibits several patterns tending to indicate that UFOs are real, represent a previously unrecognized phenomenon, and that the facts do not support the common concept of "space visitors." Five specific arguments articulated here contradict the ETH:

1. unexplained close encounters are far more numerous than required for any physical survey of the earth;
2. the humanoid body structure of the alleged "aliens" is not likely to have originated on another planet and is not biologically adapted to space travel;
3. the reported behavior in thousands of abduction reports contradicts the hypothesis of genetic or scientific experimentation on humans by an advanced race;
4. the extension of the phenomenon throughout recorded human history demonstrates that UFOs are not a contemporary phenomenon; and
5. the apparent ability of UFOs to manipulate space and time suggests radically different and richer alternatives.