Celtic music is a broad grouping of musical genres that evolved out of the folk musical traditions of the Celtic peoples of Western Europe. The term Celtic music may refer to both orally-transmitted traditional music and recorded popular music with only a superficial resemblance to folk styles of the Celtic peoples.
Most typically, the term Celtic music is applied to the music of Ireland and Scotland, because both places have produced well-known distinctive styles which actually have genuine commonality and clear mutual influences. The music of Wales, Cornwall, Isle of Man, Brittany, Northumbria and Galicia are also frequently considered a part of Celtic music, the Celtic tradition being particularly strong in Brittany, where Celtic festivals large and small take place throughout the year. Finally, the music of ethnically Celtic peoples abroad are also considered, especially in Canada and the United States.
In Celtic Music: A Complete Guide, June Skinner Sawyers acknowledges six Celtic nationalities divided into two groups according to their linguistic heritage. The Q-Celtic nationalities are the Irish, Scottish and Manx peoples, while the P-Celtic groups are the Cornish, Bretons and Welsh peoples. Sawyer also mentions the Celtiberian languages as part of P-Celtic.
The Breton musician Alan Stivell uses a similar dichotomy, between the Gaelic (Irish and Scottish) branch and the Brythonic (Breton and Welsh) group, which differentiate "mostly by the extended range (sometimes more than two octaves) of Irish and Scottish melodies and the closed range of Breton and Welsh melodies (often reduced to a half-octave), and by the frequent use of the pure pentatonic scale in Gaelic music" [1].
At issue is the lack of many common threads uniting the "Celtic" peoples listed above. While the ancient Celts undoubtedly had their own musical styles, these have grown and evolved to the point where considering any modern styles reminiscent of ancient Celtic music is misleading. There is also tremendous variation between Celtic regions. Ireland, Scotland, Wales, and Brittany have living traditions of language and music, whereas Cornwall and the Isle of Man have only revivalist movements that have yet to take hold. Galicia has no Celtic language (Galician is a Romance language closest to Portuguese), but Galician music is often claimed to be "Celtic." Thus traditionalists and most musicological scholars dispute that the "Celtic" lands have any folk connections to each other. A strong case can be made that the similarities between the various musics called "Celtic" derive more from a common origin in the vernacular music of late mediaeval and early modern Europe than from any innate Celticity.
Many critics of the idea of modern Celtic music claim that the idea is the creation of modern marketing designed to stimulate regional identity in the creation of a consumer niche; June Skinner Sawyers, for example, notes that "Celtic music is a marketing term that I am using, for the purposes of this book, as a matter of convenience, knowing full well the cultural baggage that comes with it".
Identifying "common characteristics" of Celtic music is problematic. Most of the popular musical forms now thought of as characteristically "Celtic" were once common in many places in Western Europe. Jigs were adapted from Italian music, for example, and polkas have their origin in Czech and Polish tradition.
On the other hand, there are musical genres and styles specific to each Celtic country, due in part to the influence of individual song traditions and the characteristics of specific languages. Strathspeys are specific to Highland Scotland, for example, and mimic the rhythms of the Scottish Gaelic language.