Esoteric & Occult
The UFO Files
From India to the Planet Mars
by Théodore Flournoy, tr. Daniel B. Vermilye 
Psychic contact with Mars at the dawn of the 20th century.
The Complete Works of Charles Fort
by Charles Fort [1919-33]
The premiere early 20th century compiler of accounts of strange objects in the sky, and much more ...
I Remember Lemuria
by Richard S. Shaver 
Beware the devolved tunnel-dwellers who rule the earth: the dress-rehearsal for the UFO craze.
The Flying Saucers Are Real
by Donald Keyhoe 
A classic of UFOology which slipped into the public domain,
and is also available in several formats from Project Gutenberg,
based on this etext.
Other Tongues--Other Flesh
The Secret of the Saucers
by George Hunt Williamson 
Another UFO classic which introduced many of the concepts of the field,
such as 'walk-ins'.
by Ofreo M. Angelucci edited by Ray Palmer 
By one of the first contactees, an inside view of the early UFO movement, and his visits to cosmic realms almost beyond human comprehension.
The Report on Unidentified Flying Objects
by Edward J. Ruppelt 
The memoir of the US Air Force officer who coined the acronym UFO and spearheaded the early US Air Force UFO reports such as Blue Book.
In Days To Come
by Ashtar (Ethel P. Hill) [1957?]
Please welcome Earth's new alien overlords....
We Met the Space People
by Helen Mitchell and Betty Mitchell 
The Mitchell Sisters from St. Louis meet the Space Brothers from Venus.
Life on Mars?
Since the late 19th century, the question of life on Mars
has been raised again and again.
In spite of ever-increasing scientific knowledge of the harsh
realities of the Martian surface, and
high resolution pictures of the surface, for many
the question is far from resolved.