Radio is the most widespread electronic medium in the world today. As a form of technology that is both durable and relatively cheap, radio remains central to the everyday lives of billions of people around the globe. It is used as a call for prayer in Argentina and Appalachia, to organize political protest in Mexico and Libya, and for wartime communication in Iraq and Afghanistan. In urban centers it is played constantly in shopping malls, waiting rooms, and classrooms. Yet despite its...