The term Cryptozoology was coined in 1959 by Lucien Blancou in a book dedicated to the foremost researcher of unknown animals, Bernard Heuvelmans. As the term has now become a standard part of modern vocabulary and appears in almost all dictionaries, it is defined as "the science of hidden animals". It combines the three Greek words: kryptos, zoon and logos, which mean, respectively, hidden, animal, and discourse. In 1955, Heuvelman published On the Track of Unknown Animals and the new discipline was born. By 1982, the International Society of Cryptozoology was founded at a meeting held at the Smithsonian Institution. According to this meeting, Cryptozoology concerns "the possible existence of known animals in areas where they were not supposed to occur, either now or in the past), as well as the unknown persistence of presumed extinct animals to the present time or recent past...What makes an animal of interest to cryptozoology...is that it is unexpected". To be an animal of interest, it also must have at least one trait "truly singular, unexpected, paradoxical, striking, emotionally upsetting and thus be capable of mystification" according to Bernard Heuvelman.

The most famous creatures of Cryptozoology are the spectacular and disputed Loch Ness Monster, Sasquatch and Colossal Squid. And while these legendary creatures have made the study of cryptids (as cryptozoologists call them) well known throughout the world, it is only a fraction of the hidden, un-catalogued, or out-of-place animals that have advanced this discipline. In 1812, Baron Georges Cuvier, the revered French biologist considered the father of Paleontology, declared the end of the age of zoological discovery. "There is," he said, "little hope of discovering new species [of large animals]. I hope nobody will ever seriously look for [Sea Serpents] in nature; one could as well search for the animals of Daniel or for the beast of the Apocolypse." A short seven years later, in 1819, the American tapir was found, the first of thousands of "new" animals to be uncovered in the last few centuries. Some other animals include the Giant Squid (1870s), Okapi (1901), the Komodo dragon (1912), the koupey (1937), and the coelacanth (1938). At one time even the Giant Panda was considered elusive and unknown, living in the valleys of the Himalayas, since it took 65 years between its "discovery" and the capture of a live one.

Cryptozoology represents the original way animals were studied and discovered. Researchers would go to new places and listen to local legends and reports. They would be led to amazing animals that they would document or capture to show off back in Europe at zoos or schools, where they would formally classify them. But more often than not, Cryptozoologists and their discipline is dismissed by other recognized fields like paleontologists, anthropologists and zoologists as a pseudo-science due to some of the extraordinary claims. For many, "the search for unknown animals was at best a tainted enterprise, at worst an exercise in folly."

Hoaxes also figure into the perception of Cryptozoology. From false news reports in the late-19th century to the Patterson Film today, Cryptozoologists fight an uphill battle to get their questions answered and creatures found.