This chapter evaluates the progress the three cities—New York City, Los Angeles, and Toronto—have made in reducing their greenhouse gas (GHG) emissions and the effects their efforts have had beyond these direct outcomes. As expected, tracking city-scale GHG emissions is difficult and reporting, in many cases, is inconsistent. In all three cases, city figures show that emissions are declining and at a rate that is largely consistent with longer-term goals—between 12 percent and 26 percent below baseline levels. Moreover, as the three cities work to reduce GHG emissions, they are having much broader effects on local political and administrative arrangements, other cities' efforts to govern GHG emissions, and the decisions of state and provincial governments. These catalytic effects underscore the important mobilizing role cities play in global climate change mitigation efforts.