One of the most important instruments in the traditional repertoire of Ireland, Brittany and Scotland, the fiddle (or violin - there is no physical difference) is played differently in widely-varying regional styles. It is normally tuned as GDAE. Modern performers include Kevin Burke, the late Johnny Cunningham, Christian Lemaître, Jacky Molard, James Kelly, Martin Hayes, Martin Dowling, Matt Cranitch, Frankie Gavin, Mairéad Ní Mhaonaigh, Brian MacNeill, Winnifred Horan and Tommy Peoples. Sligo fiddlers like Michael Coleman, James Morrison and Paddy Killoran did much to popularise Irish music in the States in the 1920s and 1930s.

The best-known Irish regional fiddling traditions are from Donegal, Sligo, Sliabh Luachra and Clare. Brittany and Scotland have their own regional styles, but are less centered around a particular instrument.