Eskayan is an artificial auxiliary language of the Eskaya people of Bohol, an island province of the Philippines. Its grammar is structurally similar to Visayan-Boholano, the native language of Bohol, with a lexicon that shows little relationship to any Philippine languages. While Eskayan has no mother-tongue speakers, it is taught by volunteers in at least three cultural schools in the southeast interior of the province.

Eskayan has a number of idiosyncrasies that have attracted wide interest. One of its most immediately remarkable features is its unique writing system of over 1,000 syllabic characters, said to be modeled on parts of the human body, and its non-Philippine lexicon.

The earliest attested document in Eskayan provisionally dates from 1908, and was on display at the Bohol Museum until September 2006.^{[citation needed]}

According to speakers, the Eskaya language and script were creations of Pinay, the ancestor of the Eskaya people, who was inspired by human anatomy. The Eskayan language was "rediscovered" in the early 20th century by Mariano Datahan (born Mariano Sumatra, ca. 1875–1949), a Messianic rebel soldier who transmitted it to his followers. Datahan had founded a utopian community in southeast Bohol in the aftermath of the Philippine–American War, in order to resist imperial claims and establish an indigenous nation in Bohol, and the Eskayan language and script were seen as the embodiment of this incipient national culture.

The Last Language on Earth, written by Piers Kelly in 2022, applies a systematic analysis of the Eskayan language and script to trace the history of its speakers, their folklore and religion. Kelly argues that lexical, grammatical and graphical peculiarities all lend support the traditional Eskaya belief that the language and script were created by a charismatic ancestor.^{[citation needed]}

This research further suggests that the Eskayan language emerged in the period after Spanish contact but prior to the full introduction of English after the Philippine–American War. Partial evidence of this includes the presence of "native" terms (i.e., not borrowed or calqued) for post-contact cultural categories such as pope and aeroplane. Further, the language makes semantic distinctions that are made in Spanish and English but not in Visayan (such as between moon and month). Other evidence for this can be found in Eskayan syllable structures that align with Spanish and English. It is circumstantially plausible that some Eskayan vocabulary was created by taking parallel Spanish-English-Visayan wordlists from textbooks, and replacing the Visayan layer with new vocabulary. Finally, the Eskayan script is influenced by the Roman alphabet and bears strong similarities to 19th-century Copperplate handwriting.

Indigenous constructed languages with accompanying creation myths are attested elsewhere in the world. One notable case is the Damin ceremonial language of the Gulf of Carpentaria which is said to have been the creation of the ancestor Kalthad; another are the Pandanus languages of the Medan region of Papua New Guinea.

Eskayan is a "sophisticated encryption" of the Cebuano language. It shows no lexical similarity to any of the indigenous languages of the Philippines, apart from a very few Cebuano words. Grammatically, however, it is Cebuano. Most of the words were invented, though with inspiration from Spanish and English vocabulary and phonotactics. Some Spanish words had their meanings changed, such as astro 'sun' (from 'star') and tre 'two' (from 'three').