Scientific and economic consensus points to the need for a credible and cost-effective approach to address the threat of global climate change, but the Kyoto Protocol to the U.N. Framework Convention on Climate Change appears incapable of inducing significant participation and compliance. We assess the Protocol and alternative policy architectures, with particular attention to their respective abilities to induce participation and compliance. We find that those approaches that offer cost-effective mitigation are unlikely to induce significant participation and compliance, while those approaches that are likely to enjoy a reasonably high level of implementation by sovereign states are sorely lacking in terms of their anticipated cost effectiveness. The feasible set of policy architectures is thus limited to second-best alternatives.