For more than a century, the United States has taken the lead in organizing international responses to international environmental problems. In the last two decades, however, U.S. environmental leadership has faltered. The best-known example is the lack of an effective response to climate change, underscored by the U.S. decision not to join the Kyoto Protocol. But that is not the only shortfall. The United States has also failed to join a large and growing number of treaties directed at other environmental threats, including marine pollution, the loss of biological diversity, persistent organic pollutants, and trade in toxic substances. This white paper identifies ten of these critical, pending environmental treaties and explains their impo...