Market-based environmental instruments are the most creative of the many initiatives devised to combat air and water pollution and promote biodiversity. Among these, none has attracted more attention than the burgeoning trade in environmental allowances and credits. Originally developed in the United States around 1990, these varieties of tradable instruments were globally validated by the Kyoto Protocol of 1997, which explicitly contemplates the buying and selling of environmental allowances and credits among both sovereign states and corporate entities. Despite U.S. opposition to the Kyoto...