Cryptozoology is a pseudoscience and subculture that searches for and studies unknown, legendary, or extinct animals whose present existence is disputed or unsubstantiated, particularly those popular in folklore, such as Bigfoot, the Loch Ness Monster, Yeti, the chupacabra, the Jersey Devil, or the Mokele-mbembe. Cryptozoologists refer to these entities as cryptids, a term coined by the subculture. Because it does not follow the scientific method, cryptozoology is considered a pseudoscience by mainstream science: it is a branch of neither zoology nor folklore studies. It was originally founded in the 1950s by zoologists Bernard Heuvelmans and Ivan T. Sanderson.

Scholars have noted that the subculture rejected mainstream approaches from an early date, and that adherents often express hostility to mainstream science. Scholars studying cryptozoologists and their influence (including cryptozoology's association with Young Earth creationism) noted parallels in cryptozoology and other pseudosciences such as ghost hunting and ufology, and highlighted uncritical media propagation of cryptozoologist claims.

As a field, cryptozoology originates from the works of Bernard Heuvelmans, a Belgian zoologist, and Ivan T. Sanderson, a Scottish zoologist. Notably, Heuvelmans published On the Track of Unknown Animals (French: Sur la piste des bêtes ignorées) in 1955, a landmark work among cryptozoologists that was followed by numerous other similar works. In addition, Sanderson published a series of books that contributed to the developing hallmarks of cryptozoology, including Abominable Snowmen: Legend Come to Life (1961). Heuvelmans himself traced cryptozoology to the work of Anthonie Cornelis Oudemans, who theorized that a large unidentified species of seal was responsible for sea serpent reports.

Cryptozoology is 'the study of hidden animals' (from Ancient Greek: κρυπτός, kryptós "hidden, secret"; Ancient Greek ζῷον, zōion "animal", and λόγος, logos, i.e. "knowledge, study"). The term dates from 1959 or before— Heuvelmans attributes the coinage of the term cryptozoology to Sanderson. Following cryptozoology, the term cryptid was coined in 1983 by cryptozoologist J. E. Wall in the summer issue of the International Society of Cryptozoology newsletter. According to Wall "[It has been] suggested that new terms be coined to replace sensational and often misleading terms like 'monster'. My suggestion is 'cryptid', meaning a living thing having the quality of being hidden or unknown ... describing those creatures which are (or may be) subjects of cryptozoological investigation."

The Oxford English Dictionary defines the noun cryptid as "an animal whose existence or survival to the present day is disputed or unsubstantiated; any animal of interest to a cryptozoologist". While used by most cryptozoologists, the term cryptid is not used by academic zoologists. In a textbook aimed at undergraduates, academics Caleb W. Lack and Jacques Rousseau note that the subculture's focus on what it deems to be "cryptids" is a pseudoscientific extension of older belief in monsters and other similar entities from the folkloric record, yet with a "new, more scientific-sounding name: cryptids".

While biologists regularly identify new species, cryptozoologists often focus on creatures from the folkloric record. Most famously, these include the Loch Ness Monster, Champ (folklore), Bigfoot, the chupacabra, as well as other "imposing beasts that could be labeled as monsters". In their search for these entities, cryptozoologists may employ devices such as motion-sensitive cameras, night-vision equipment, and audio-recording equipment. While there have been attempts to codify cryptozoological approaches, unlike biologists, zoologists, botanists, and other academic disciplines, however, "there are no accepted, uniform, or successful methods for pursuing cryptids". Some scholars have identified precursors to modern cryptozoology in certain medieval approaches to the folkloric record, and the psychology behind the cryptozoology approach has been the subject of academic study.

Few cryptozoologists have a formal science education, and fewer still have a science background directly relevant to cryptozoology. Adherents often misrepresent the academic backgrounds of cryptozoologists. According to writer Daniel Loxton and paleontologist Donald Prothero, "[c]ryptozoologists have often promoted 'Professor Roy Mackal, PhD.' as one of their leading figures and one of the few with a legitimate doctorate in biology. What is rarely mentioned, however, is that he had no training that would qualify him to undertake competent research on exotic animals. This raises the specter of 'credential mongering', by which an individual or organization feints a person's graduate degree as proof of expertise, even though his or her training is not specifically relevant to the field under consideration." Besides Heuvelmans, Sanderson, and Mackal, other notable cryptozoologists with academic backgrounds include Grover Krantz, Karl Shuker, and Richard Greenwell.

In a 2025 interview with science writer Sharon Hill "Cryptids have become cutified" ... The reason why cryptids are seeing a resurgence are because of the Internet, for example, the Flatwoods monster is seen in over 33 video games, but the real reason according to Hill is because for a while cryptids were thought to be real animals that some people had assigned magical powers to, and with some investigation the hope was that the magic could be stripped away and they would discover a real, perhaps unknown animal. “One of the reasons why I think that fell apart completely was because the International Society of Cryptozoology fell apart completely, so there were no longer any gatekeepers as of the early 1990’s to say ‘a cryptid is these animals that we are studying because we think it’s got a zoological basis’, those people were gone ... they were quite old, they died and there was nobody there to take over that gatekeeping aspect although some people tried. ... Then you saw an explosion of amateurs in the 2000s ... they became researchers that connected via the Internet. Now they start making media they can publish themselves ... it started to hit a younger and younger generation ... who love these creatures ... now everything can be a cryptid.”