To many, the terms ecosystem services and ecosystem valuation sound obscure and complex. But for a growing number of economists, government officials, and financiers, quantifying the benefits of clear-running streams, standing forests, and other natural processes is an idea whose time has come. The Economist (2005) recently devoted a cover story to the challenges of putting a proper value on ecological services. Last year the World Bank and the National Research Council both issued reports on assessing nature's services. These efforts followed on the heels of the international Millennium Ecosystem Assessment, which enjoyed international support.