In 1979, the nuclear reactor at Three Mile Island in Pennsylvania suffered a partial meltdown and sent hundreds of thousands of residents fleeing as radiation leaked into the atmosphere. The resulting media coverage made "Three Mile Island" into an international symbol of the dangers of nuclear energy, prompted nationwide opposition to nuclear power, and shut down the nuclear industry for more than a decade. Yet, Three Mile Island was not the first accident of its kind. In 1966, the Fermi reactor outside Chicago experienced a partial meltdown followed by a failure of the automatic shut-down system. Officials discussed evacuation plans for area residents as they tried to avert the possibility of a secondary accident.The Fermi accident was no secret: the press was alerted as it was happening. But newspapers, including the New York Times, gave the episode only perfunctory coverage, mainly repeating company spokespeople's assurances that the reactor would soon be up and running.Why did the Fermi accident not produce the public crisis that Three Mile Island did? Because it was viewed through different frames, says William Gamson (1988). At the time of the Fermi accident, nuclear power was covered by the press mainly in terms of a "faith in progress" frame that viewed nuclear power unequivocally as a boon to technological development and human progress. By Three Mile Island, however, media stories about nuclear power were less confident about nuclear power's safety and effectiveness. The stage was already set for a critical and alarmist interpretation of the accident. The concept is appealing for several reasons. The term "frame" reminds us that persuasion works in part by demarcating and punctuating important aspects of reality, that is, by making events and circumstances intelligible as much as by advancing a compelling point of view. If we think of a frame as the structure of a building rather than the perimeter of a picture 2 (Gamson 2004), the concept also points to the deeper logics structuring political contention.While actors instrumentally frame situations so as to press their case, their very understanding of what is instrumental is shaped by taken for granted frames. In that sense, frames are both strategic and set the terms of strategic action.In this chapter, we focus on framing in social movements. The theoretical and empirical literature on the topic is now extensive and, in many cases, sophisticated. But it remains thin on the relations between frames and their political and cultural contexts. We do not know enough about why activists choose the frames they do, what aspects of the environment shape frames'effectiveness, and what impacts frames have on institutions outside the movement. Several factors are probably to blame. The single case orientation of much of the work on framing has made it difficult to generalize about causes and effects. A tendency to view frames as emergent, that is, as constructed in and through movement work, has been valuable in capturing the dynamic quality of frames but has ...