This article argues that the decisive part of the interaction between social movements and political authorities is no longer the direct, physical confrontation between them in concrete locations, but the indirect, mediated encounters among contenders in the arena of the mass media public sphere. Authorities react to social movement activities if and as they are depicted in the mass media, and conversely movement activists become aware of political opportunities and constraints through the reactions (or non-reactions) that their actions provoke in the public sphere. The dynamics of this mediated interaction among political contenders can be analyzed as an evolutionary process. Of the great variety of attempts to mobilize public attention, only a few can be accommodated in the bounded media space. Three selection mechanisms-labelled here as "discursive opportunities"-can be identified that affect the diffusion chances of contentious messages: visibility (the extent to which a message is covered by the mass media), resonance (the extent to which others-allies, opponents, authorities, etc.-react to a message), and legitimacy (the degree to which such reactions are supportive). The argument is empirically illustrated by showing how the strategic repertoire of the German radical right evolved over the course of the 1990s as a result of the differential reactions that various strategies encountered in the mass media arena. As the work of Charles Tilly 1 has shown us, before the advent of the modern, democratic nation-state, interactions between protesters, authorities, and publics were mostly localized, immediate, and direct. People would gather at the premises of a merchant, a landowner, or the seat of a local authority, and make their demands audible and visible by way of chants, slogans, petitions, or direct action such as the seizure of grain or physical attack on the wrongdoer. The power-holders thus addressed would respond in equally immediate and direct ways, by having the local police or private strongmen disperse the protesters, receiving a delegation to hear and respond to their grievances, or by themselves addressing the crowd, to rebut criticism or perhaps to announce concessions. Usually, neither of the parties directly involved in