Editors' Summary: Perhaps the most sinister environmental threats include those that are least perceptible. One such threat is the large scale extinction of biological species, with ominous implications for a shrinking gene pool and multiplier effects throughout the food web whenever key species are lost. This Comment analyzes one of the principal international responses to this threat, the Convention on International Trade in Endangered Species. Although the Convention is widely hailed as a success, the Comment points out that it imperfectly addresses the root causes of species extinction, and the evidence of effective implementation of even the limited mission of the Convention is spotty. The Comment reviews the United States' implementation of the Convention, principally through the Endangered Species Act, and concludes that much more analytical work and enforcement effort is needed both in the United States and abroad.