An independent daughter-branch in the family of Indo-European languages, along with Germanic, Italic, Indo-Iranian and the like, the Celtic languages emerged in proto-form around 1400 B.C. in common with the other main western branches of Indo-European. The Celtic “homeland” of the early period appears to have been in southern and eastern Europe, although major migrations beginning about 1000 B.C. carried Celtic speakers as far as the Iberian peninsula and central Anatolia. The great period of Celtic expansion in western Europe, however, dates from the Hallstatt period, around 700 B.C. As the Romans expanded around the Mediterranean from that period onwards, the Celts expanded throughout western Europe and into the British Isles. This great period of Celtic expansion comes to an end in the first two centuries A.D. under the combined pressure of Roman and Germanic expansionism and is in many respects well recorded in Roman historical sources such as Caesar’s Gallic Wars.

The Celtic languages that survived into the modern period – Welsh, Irish, Breton, Scottish Gaelic, Manx, and Cornish (the last two only recently extinct) – are spoken as primary languages by about a million people, although easily twice that number might be counted as fluent speakers. Irish, Welsh, Scottish Gaelic, and Breton have extensive literatures and Irish and Welsh a lively contemporary literary scene. The collected traditional folklore resources of Celtic-speaking Europe are vast, and a century of concentration on collection has left enormous archives of unedited and unstudied oral folk material. The demographic and cultural pressure of English and French seems likely to ensure that Irish, Welsh and Breton remain minority languages, but neither Irish nor Welsh is in danger of dying out. As for Breton, it is currently at serious risk, but continues to survive.

The scholarly interest of the Celtic languages is twofold: first, they have a unique surviving literary and recorded peasant folk tradition, and second, in spite of their extensive literary remains, they are still relatively unstudied from the standpoint of comparative Indo-European linguistics, literature, and culture, owing to the small number of investigators who have been trained to study them. No other major surviving branch of the Indo-European languages has received less scholarly attention to date; the field is hardly even surveyed and important discoveries remain to be made even by relatively inexperienced investigators.

Once the Indo-European nature of the Celtic languages (and especially their close connection with the Italic branch) were discovered by Bopp and Zeuss in the early 19th century, scholarly study began at German universities and elsewhere on the continent, and in the British Isles (Oxford and Cambridge). Rising nationalist feeling in the Celtic areas of Britain led to the establishment of new universities (University College of Wales at Aberystwyth, with some instruction in the medium of Welsh) and other learned organizations (the Royal Irish Academy, the School of Irish Studies). Journals were founded (Zeitschrift für Celtische Philologie, Etudes Celtiques, Journal of the Royal Society of Antiquaries of Ireland, Eriu) and systematic attention began to be devoted to recovering, editing, and translating manuscript material in the Celtic languages. Great impetus was given to Celtic Studies by the founding of the Royal University of Ireland in 1880, later (1908) renamed the National University of Ireland, and, after Ireland became independent (1922), by the establishment of the Irish Folklore Commission and the Dublin Institute for Advanced Studies. Irish, Scottish, and Welsh universities have continued to develop and strengthen Celtic Studies. In recent years the Center for Advanced Welsh and Celtic Studies has been established in Aberystwyth, Wales. Brittany has acquired two university campuses, at Rennes and Brest, and Breton has emerged as an approved area of study in French universities.