Celtic studies or Celtology is the academic discipline occupied with the study of any sort of cultural output relating to the Celtic-speaking peoples (i.e. speakers of Celtic languages). This ranges from linguistics, literature and art history, archaeology and history, the focus lying on the study of the various Celtic languages, living and extinct. The primary areas of focus are the six Celtic languages currently in use: Irish, Scottish Gaelic, Manx, Welsh, Cornish, and Breton.

As a university subject, it is taught at a number of universities, most of them in Ireland, the United Kingdom, or France, but also in the United States, Canada, Australia, Germany, Poland, Austria and the Netherlands.

Written studies of the Celts, their cultures, and their languages go back to classical Greek and Latin accounts, possibly beginning with Hecataeus in the 6th century BC and best known through such authors as Polybius, Posidonius, Pausanias, Diodorus Siculus, Julius Caesar and Strabo. Modern Celtic studies originated in the aftermath of the Gutenberg Revolution, when many of these classical authors were rediscovered, mass produced using the printing press, and translated into vernacular languages.

Academic interest in Celtic languages grew out of comparative and historical linguistics, which were established at the end of the 18th century. In the 16th century, Renaissance humanist George Buchanan, a native speaker of the Scottish Gaelic language, comparatively studied the Goidelic languages. The first major breakthrough in Celtic linguistics came with the publication of Archaeologia Britannica (1707) by the Welsh scholar Edward Lhuyd, who was the first to recognise that Gaulish, Welsh, Cornish, and Irish all belong to the same language family. Lhuyd also published an English translation of a study by Paul-Yves Pezron into Gaulish.

In 1767 James Parsons published his study The Remains of Japhet, being historical enquiries into the affinity and origins of the European languages. He compared a 1000-word lexicon of Irish and Welsh and concluded that they were originally the same, then comparing the numerals in many other languages.

The second big leap forwards was made when Sir William Jones postulated that Sanskrit, Avestan, Greek, Latin and many other languages including "the Celtic" derived from a common ancestral language. This hypothesis, published in The Sanscrit Language (1786), would later be hailed as the discovery of the Indo-European language family, from which grew the field of Indo-European studies.

Although Jones' trail-blazing hypothesis inspired numerous linguistic studies, it was not until Bavarian linguist Johann Kaspar Zeuss's monumental Grammatica Celtica (volume 1, 1851; volume 2, 1853) that any truly significant progress was made. Written in Latin, the work draws on the earliest Old Irish, Middle Welsh and other Celtic primary sources to construct a comparative grammar, which was the first to lay out a firm basis for Celtic philology. Among his many other achievements, Zeuss was able to decipher and explain Old Irish verbal and grammatical rules and also definitively linked the Celtic languages to the Indo-European language family

German Celtic studies (Keltologie) is seen by many as having been established by Johann Kaspar Zeuss (1806–1856). In 1847, he was appointed professor of linguistics at the Ludwig Maximilian University of Munich. Until the middle of the 19th century, Celtic studies progressed largely as a subfield of linguistics. Franz Bopp (1791–1867) carried out further studies in comparative linguistics to link the Celtic languages to the Proto-Indo-European language. He is credited with having finally proven Celtic to be a branch of the Indo-European language family. From 1821 to 1864, he served as a professor of oriental literature and general linguistics in Berlin.^{[citation needed]}