Preventing the spread of nonnative invasive species is an international public good. Some categories of invasive species—such as diseases of humans and livestock—are addressed by international agreements that coordinate efforts to reduce their spread. In contrast, invasive species that primarily cause environmental impacts are managed almost exclusively at the national level. Control of environmental invaders is internationally undersupplied because the efforts of nations that do invest to prevent their spread are undercut by nations that do not. Addressing this problem will require international cooperation. We identify the international approach to controlling human diseases as a model that could provide institutions and mechanisms to map the spread of environmental invaders and assess the risks they impose. This would allow individual nations to manage potential vectors of invasion. Because such a system is unlikely to be implemented in the near future, we make recommendations for intermediate steps, including the widespread adoption of existing risk assessments and importation standards.