How do international border cities interact with one another about sustainable development? Existing research suggests international networks play a role in linking cities in a global dialogue about sustainability. Within individual cities, local networks including government agencies and nongovernmental organizations also play a role in sustainability discussions. This research suggests both perspectives on networks can inform the study of how international border cities approach interaction about sustainable development. Detroit and Windsor are examined as a case study. Interviews with government officials and nongovernmental organizations in both cities illuminate how Windsor and Detroit approach sustainable development in different ways. Social network analysis is used to identify organizations bridging the border between Canada and the United States. The research offers new propositions about how networks contribute to economic, environmental, and social policy coordination in international border regions.