All parties to the Kyoto agreement have a responsibility to limit greenhouse gas emissions according to their capacity. Through a quantitative international comparison of economic, institutional, and technological factors, this paper seeks to identify some of the determinants of countries’ mitigative capacity and actions.The paper finds that three economic factors – income, abatement cost and opportunity cost – interact to determine mitigative capacity:a higher national per capita income means a higher mitigative capacityhigher costs of abatement are found to be an important factor in translating capacity into actual mitigation.In addition, however, institutional factors that promote mitigative capacity are important. These include the effectiveness of government regulation, clear market rules, a skilled work force and public awareness. Technology also plays a critical capacity role, including the ability (due to human capital factors) to absorb existing climate-friendly technologies or to develop innovative ones.From this analysis, the paper notes that economic factors alone do not explain why some countries with high mitigative capacity act under the Kyoto Protocol while others do not. Additional barriers to translating capacity into actual mitigation include:political willingness, which is shaped by a variety of cultural, political and institutional factors; and the relationship between the expert and lay communities, risk perception, industry-regulator relationships, the power and influence of interest groups, as well as a nation’s historical culture and self-perception.