Celtic music means two things mainly. Firstly, it is the music of the peoples calling themselves Celts (a non-musical, primarily political definition), as opposed to, say, "French music" or "English music." Secondly, it refers to whatever qualities may be unique to the musics of the Celtic Nations (a musical definition). Some insist that different ostensibly Celtic musics actually have nothing in common – such as Geoff Wallis and Sue Wilson in their book The Rough Guide to Irish Music – whereas others (such as Alan Stivell), say there is.
Often, 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; however, it is notable that Irish and Scottish traditional musicians themselves avoid the term "Celtic music," except when forced by the necessities of the market. These styles are known because of the importance of Irish and Scottish people in the English speaking world, especially in the United States, where it had a profound impact on American music, particularly bluegrass and country music. The music of Wales, Cornwall, the Isle of Man, Brittany, Galicia, Cantabria and Asturias and Northern Portugal are also considered Celtic music, the tradition being particularly strong in Brittany, where Celtic festivals large and small take place throughout the year, and in Wales, where the ancient eisteddfod tradition still occurs. Additionally, the musics of ethnically Celtic peoples abroad are vibrant, especially in Canada and the United States.
There is also tremendous variation between "Celtic" regions. Ireland, Scotland, and Brittany have living traditions of language and music, and there has been a recent major revival of interest in Wales. However, Cornwall and the Isle of Man have only small-scale revivalist movements that have yet to take hold. Galicia has no Celtic language today (Galician is a Romance language descending from Galician-Portuguese, although all the Western part of the Peninsula had Celtic languages in pre-Roman times, as did England, France, and parts of Italy and Turkey), but Galician music is often claimed to be "Celtic." The same is true of the music of Asturias, Cantabria, and that of Northern Portugal (some say even traditional music from Central Portugal can be labeled Celtic). Thus traditionalists and 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 medieval and early modern Europe than from any innate "Celticity". But some call that giving too much importance to basic material, saying that the originality of a music is in the subtle transformation, by a people or a group of peoples, of material shared by larger communities.
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". The so-called "marketing" or "show-business" creation was popularized by the idealistic man who first (late 1960s) blended the music of all the Celtic countries with a modern touch in his recordings and concerts: the Breton Alan Stivell. Although this composer is one of the main modern promoters of this kind of music, he did not create the term.
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 it has been hypothesized that they mimic the rhythms of the Scottish Gaelic language.
The first attempts of a "Pan-Celtic music" were made somehow by the Breton Taldir Jaffrennou, having translated into Breton songs from Ireland, Scotland, Wales and made them popular in Brittany between the two world wars.
In the 50s, the Breton Alan Cochevelou (future Alan Stivell) played a mixed repertoire (from the main Celtic countries) on Celtic harp. In the 60s, the Breton bagadoù fused Breton music mainly with Scottish music.
But it's only in the mid-60s that occurred a true concept of pan-Celtic music, with the beginnings of Alan Stivell, fusing the musics of the Celtic nations with many different genres (Rock, Symphonic, Electronic, etc. ).
Other modern adaptations in the 1960s were those of artists such as Fairport Convention, Pentangle and Steeleye Span in England, Horslips in Ireland, later Planxty and Clannad, some of whom are still now exploring new kinds of Celtic fusion, combining traditional acoustic instruments with amplified ones, adding modern beat patterns, and composing modern harmonies for traditional tunes.
Later, beginning in 1982 with The Pogues' invention of Celtic folk-punk, there has been a movement to incorporate Celtic influences into other genres of music. Bands such as Seven Nations and Needfire do American adaptions in the form of Celtic rock. Composer Ciarán Farrell blends classical influences with rock, jazz, folk and traditional Irish styles, using different combinations of instruments and orchestras to play his music. Marxman, an Irish-Jamaican hip hop group that gained notoriety in Britain in the late 1980s and was banned from the BBC for including I.R.A. slogans in their music, sampled traditional Celtic instruments in several of their songs. Sinéad O'Connor has also been active in the fusion movement and incorporated a wide range of modern and traditional influences into her music. Enya adds her vocal sound to music with Celtic sounds and themes on her album The Celts; Moya Brennan, former lead singer of Clannad, was featured in the soundtrack of the film King Arthur; and Loreena McKennitt made an album called The Book of Secrets where she first travelled and researched the places that inspired the Celtic style of music on the album. More recently, the Irish choral group Anúna have been very successful with their unusual blend of choral, Celtic and classical music.
In 1978 Runrig recorded an album in Scottish Gaelic. In 1992 Capercaillie recorded "A Prince Among Islands", the first Scottish Gaelic language record to reach the UK top 40. Since about 2005, Oi Polloi (from Scotland) have recorded in Scottish Gaelic. Mill a h-Uile Rud (a Scottish Gaelic punk band from Seattle) recorded in the language in 2004.
Several contemporary bands have Welsh language songs, such as Ceredwen, which fuses traditional instruments with trip-hop beats, the Super Furry Animals, Fernhill (band), and so on (see the Music of Wales article for more Welsh and Welsh-language band).
Today there are Celtic-influenced sub genres of virtually every type of popular music, from electronica to rock and metal, hip hop to punk rock, new age, pop, and even reggae. Collectively these modern interpretations of Celtic music are sometimes referred to as Celtic fusion.