Transboundary pollution in North America has received international attention for over 90 years. Famous, or infamous, examples from the past include the sulfur dioxide emitted by a smelter near Trail, British Columbia in the 1920s; the salinization of the Colorado River in the 1960s; and the contribution of U.S. power plants to Canadian acid rain in the 1980s. Despite a series of bilateral agreements and institutions addressing particular concerns and some notable successes, transboundary pollution continues. Indeed, every section of both borders seems to have its own notorious problem. San Diegans complain that sewage from Tijuana befouls their beaches; Texans accuse power plants in Coahuila of clouding the skies over Big Bend National Park; Mexicans protest against proposals to site waste disposal facilities in South Texas; Ontario argues that U.S. power plants cause most of its air pollution; and Alaskans worry about the downstream effects of mining in British Columbia. Moreover, thousands of sources, on both sides of the border, pollute shared bodies of water such as the Great Lakes and the Rio Grande and shared airsheds such as that over El Paso, Texas, and Ciudad Juárez, Mexico.

What, if anything, should the North American Commission for Environmental Cooperation (CEC) do about transboundary pollution? In particular, should it coordinate the work of the bilateral institutions and fill gaps in their coverage? After evaluating how the CEC has handled issues of transboundary environmental harm, this Article concludes that the answer to this question is a qualified: "No." The CEC should not try to oversee the work of the bilateral institutions, and it should address only one important type of transboundary pollution outside their jurisdiction: pollution that directly affects all three countries.