The blues is a vocal and instrumental form of music based on the use of the blue notes, often with a repetitive twelve-bar structure, which evolved in the United States in the communities of former African slaves. Canadian blues refers to the blues and blues-related music (. blues-rock, folk blues, etc.) performed by blues bands and performers in Canada. In Canada, there are hundreds of local and regionally based Canadian blues bands and performers. As well, there is a smaller number of bands or performers that have achieved national or international prominence. These bands and performers are part of a broader Canadian "blues scene" that also includes city or regional blues societies, blues radio shows, and blues festivals.