The certification of the environmental and social characteristics of a product's production process is emerging as a significant transnational, nongovernmental, market-based approach to environmental regulation and development. Using conventions analysis and commodity network analysis, this article examines the political ecology of one such market intervention. After only a decade, environmental certification of forests has spread to cover a significant portion of the world's logged forests, major wood retailers increasingly require it, and international environmental organizations strongly support it. In Mexico, where 12 percent of the wood harvest is certified, certification requires forest managers to make substantial improvements to the social and environmental aspects of forest management. Actors in the Mexican wood commodity network include forest villagers, forest managers, wood processors, government regulators, and transnational wood retailers. These actors express an array of environmental concerns, social values, and interests in price and market share. The big retailers, however, are the most powerful actors in the commodity network, and their demands for high volumes and low prices dominate. As a result, forest certification has so far failed to generate prices that permit forest managers to cover the costs of certification and its required forest management improvements; the instrument imposes requirements on southern producers without rewarding them for their increased efforts. In addition to the equity issues, these features of the commodity network limit the adoption of forest certification—and the forest management improvements it generates—to only the largest forest management operations in Mexico. The case of Mexico suggests broader limitations to nongovernmental, market-based approaches to environmental governance and development. These need to be less naïve about the ability of product certification to insert values in markets governed by powerful actors like retailers. Including rules modeled on Fair Trade will extend their reach, equity, and efficacy; nevertheless, voluntary market-based instruments cannot replace a more direct government role in environmental regulation and development projects.