Climate policy is complicated. For a treaty to be beneficial, one must think through carefully how it will work, once it is implemented. Crucial questions include the following: How should an international treaty be designed? Should one negotiate commitments for a five-year period, or for much longer? Assuming that the treaty specifies aggregate or country-specific emission caps, what should these caps be and how should they change over time? How should the agreement be updated once policymakers, scholars, and the public learn more about the severity of the climate-change problem, or about the effects of the policy? Can the treaty be designed to encourage investments in "green" abatement technology or renewable energy sources? Finally, how can one motivate countries to participate and comply with such an agreement?