This Project compares, under an institutionalist perspective, two distinct regional projects: The European Union - a product of a process initiated in the 1950 s, with higher level of institutionalization and delegation to supranational bodies and with also more member states, and the North American Free Trade Agreement (Nafta) - a more recent venture, of intergovernmental character, with emphasis on mechanisms of dispute resolution, less states and sharper differences between the parties, where the logic of the market seems to lie above environmental ethics - regarding the incorporation of an environmental agenda within regional institutions, as well as the management of this agenda. Such analysis is performed through the study of the projects institutional design. Special attention is given to institutions, bodies, actors and mechanisms dealing with environmental policies establishment, execution and enforcement. The results obtained indicate what does Nafta and EUs institutional designs can tell about the incorporation and treatment given by these regional arrangements to environmental affairs.