Societies across the globe strive to achieve water security—that is, assure access to sufficient water of acceptable quality for humans and the environment for changing, sustainable societies and ecosystems. But rapid and significant changes in environmental and social systems complicate attempts to assure water-secure conditions. This challenge is further magnified by transboundary conditions—while landscapes and physical processes disregard political borders, human institutions managing these resources often lack the traditions and capital for ensuring resilient, community-based responses to water shortage and contamination. This review highlights how features of community resilience contribute to enhancing transboundary water security using nine examples from the U.S.–Mexico border region. The cases demonstrate how public participation, adaptivity and flexibility, and social mobilization to promote equity and justice help to nurture and maintain community resilience, to the benefit of transboundary water security.