Originally published in 1961, the book—often referred to by enthusiasts as the "Bigfoot Bible"—presents an anthropological and zoological look at unidentified, sub-human primates. Relying on 30 years of collected evidence, maps, and footprint photographs, Sanderson argues that up to four distinct types of these creatures still exist and walk the Earth. 

The book details how global sightings are not isolated myths but are instead widespread across regions ranging from the high Himalayas of Tibet to the dense Klamath forests of Northern California. Sanderson covers a variety of regional cryptids—including Sasquatch, Yeti, Oh-Mah, and the Russian Almasty—analyzing historical reports, fossil records of ancient apes, local folklore, and physical geography. Ultimately, he uses his scientific background to offer compelling theories on how these hominids have successfully evaded modern capture or preservation in museums.