The 21st Century is the century of transboundary crises. The 2006 European blackout, the financial crisis of 2007-8, Ebola outbreaks, the wildfires of 2017 and 2018, and the COVID-19 pandemic are examples of transboundary crises, ‘characterized by the potential to cross geographic and functional boundaries, jumping from one system to another’. They have shaped, and will continue to shape, social life, and they are exacerbated by the planetary climate change crisis. Poverty and inequality, strained health services, struggling economies, disrupted mobilities, extreme weather events are felt across the boundaries of countries, organisations, and communities. Transboundary crises are ‘the ultimate nightmare’ for crisis managers, because they cut across multiple domains and have multiple manifestations, escalate rapidly, and are hard to predict in onset and evolution. There are multiple actors with conflicting responsibilities, and there are no ready-made solutions. It is, therefore, important to strengthen transboundary resilience, but how?