The Climate Convention calls for stabilization of atmospheric concentrations of greenhouse gases. This paper considers the issues that must be faced in formulating a plan to meet any such target, using a proposed CO2 level of 550 ppmv as an example. We hypothesize a set of "necessary conditions" for such a goal to be achievable, and test set of possible forms of agreement against them using the MIT Emissions Prediction and Policy Assessment (EPPA) model. The results highlight the importance of emissions trading to the feasibility of such a target, and the need for an agreement that can adapt efficiently over time to changing relative economic circumstances in participating nations. / Includes bibliographical references (p. 19). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/)