What are the most important transnational governance arrangements for environmental policy in North America? Has their proliferation facilitated a transition towards integrated continental environmental policy, and if so, to what degree is this integration irreversible? These governance arrangements are diverse and evolving, consisting of binational and trinational organizations created decades ago by treaties and groups of stakeholders--with varying degrees of formalization--who work together to address issues that no single country can alone. Together they provide leadership in numerous...