On December 17, 1992, Canada, Mexico, and the United States entered into a historical trade pact called the North American Free Trade Agreement (NAFTA). It aims to increase trade by expanding market access and reducing investment barriers across North American borders. Of the many aspects of the debate in the United States over the ratification of NAFTA, none received as much attention as the potential impact of the agreement on the environment. A number of issues including labor market disruptions fueled intense debate over NAFTA, especially in the United States. But no issue received as much attention as the impact of NAFTA on the environment. Debate focused on (1) possible threats posed to previously signed U.S. domestic environmental laws and international environmental agreements; (2) concern that harmonization of environmental standards would result in acceptance of the least common denominator; and (3) fear...