This article presents ethnographic work on open mic nights in Edinburgh, a hitherto under examined activity that lies in the hinterland of professional live music and serves as a junction between professional and amateur practice. It proceeds from the theoretical context of different musical “worlds”, notably the difference between “folk” and “commercial” popular music, to provide a basic typography of the different types of open mic. These intersect to varying degrees with the wider music “scene”, allowing for contact between musicians at different points on the scale of amateur to professional. Open mics also differ from other forms of “open” activity like folk sessions in that they face towards the commercial popular world, as exhibited in the use of microphones and the privileging of individual performers. The host is responsible for maintaining the explicit rules, which vary, and the implicit code of a supportive atmosphere, which is a common factor and takes precedence over other rules.