Shortly after the first commercial radio broadcast in 1920, the medium's popularity exploded and the number of stations on the dial grew tremendously. By 1930, however, a mere 10 years after the first radio broadcast occurred, the industry was dominated by large, commercial stations who sold advertising time in a variety of forms and were operated to generate profit. Because of the nature of broadcasting organizations and markets, explanations based on competitive dynamics and organizational fitness cannot explain this dramatic change in the broadcasting industry. In the absence of a competitive advantage, I argue that this concentration was the result of institutional shifts in legitimate organizational practices and the political environment in which broadcasters operated. (Contains 1 figure, 3 tables and 1 note.)