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 areas of environmental concern, including invasive species, energy efficiency, water, and terrestrial and aquatic wildlife. This book explores these arrangements, examining features such as stakeholder inclusion, organizational activities and functions, and issue comprehensiveness. Overall, the contributors report an underdeveloped policy architecture consisting of fragmented regional transnational networks of stakeholders and underfunded binational and trinational organizations. They also show evidence of substantial policy entrepreneurship and a vibrant informal underbelly to North American environmental governance, which will be vital in the challenging days ahead.