This chapter compares regulations that address the risks of air pollution—one of the most critical dimensions of environmental regulation. It specifically examines the policies in the United States and Europe and their decisions toward the health and environmental risks of mobile (vehicular) source pollutants, ozone-depleting chemicals, and global climate change. The politics of global climate change reveals a very divergent pattern. In this case, the preferences of American policy makers were more polarized than in Europe. American public policies toward the risks of global climate change have been significantly affected by partisan differences, which increased substantially during the 1990s. By contrast, European policies toward global climate change have been much less affected by differences in the political preferences of center-left and center-right policy makers.