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. The definition is further complicated by the fact that Irish independence has allowed Ireland to promote 'Celtic' music as a specifically Irish product. In reality, the terms 'Scots/Scottish' and 'Irish' are purely modern geographical references to a people who share a common Celtic ancestry and consequently, a common musical heritage.

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 (Spain) and 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.

Divisions

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. Musician Alan Stivell uses a similar dichotomy, between the Gaelic (Irish/Scottish/Manx) branch and the Brythonic (Breton/Welsh/Cornish) 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."

Definition debate

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, the actual sound of their music remains a complete mystery.