While movement activists spend much of their time and energy trying to change the world, our theoretical and empirical knowledge in this field is still relatively poor. In Social Protest and Policy Change, Marco Giugni offers a systematic and empirically grounded analysis of the impact of three major contemporary movements on public policy. Using a comparative and historical perspective, Giugni argues that a social movement’s policy impact is facilitated by the presence of favorable political opportunity structures, coupled with the presence of institutional allies among the elites, and a favorable public opinion. Furthermore, the very content of a movement’s demands plays a role, insofar as the power holders are often more willing to make concessions on certain issues than on others. Within a unique body of original data the author incorporates a historical overview of the mobilization of the ecology, antinuclear, and peace movements in the United States, Italy, and Switzerland. He presents the results of time-series analyses and reveals the combined effects of protest, political alliances, and shifts in public opinion on movements which do not address issues posing too serious a threat to the power holders.