The Commission for Environmental Cooperation (CEC) has a mandate to monitor the environmental effects of the North American Free Trade Agreement (NAFTA). This paper describes the CEC process in developing an analytic framework for assessing these effects. It gives an overview of conclusions
drawn from more than 50 studies conducted so far, and comments on lessons learned in terms of methodology and data, environmental quality, and environmental policy results. The conclusions highlight the major lesson: environmental effects have been neither very bad nor very good and are policy
dependent. After 11 years, the foundations for mutually supportive trade, environment, and economic policies have been laid; the outcome will depend on political will within the NAFTA area.