China is home to nearly half of the world's 50,000 large dams, which provide irrigation, flood protection, and hydroelectricity. Most of these projects involve substantial population displacement, which can disrupt social capital, the webs of interdependence and support that community members maintain with one another through relationships of trust and reciprocity. We use new empirical evidence to examine the association between dam-induced displacement and social capital in China and interpret our findings in the context of social-ecological resilience theory. Our focus is on agricultural households on the Upper Mekong River, where four large hydropower dams have been constructed over the past twenty years.Our broad finding is that resettlement is associated with diminished social capital, as measured by two key indicators: inter-household exchange of financial resources, and interhousehold exchange of agricultural labor. These effects differ across the four dam sites in the study based on local economic conditions and changes in resettlement policy. We find that population resettlement is associated with markedly lower levels of agricultural labor exchange. In an economically under-developed setting, this reduces the depth and breadth of social support that agricultural households rely on to produce crops for subsistence and income. This in turn diminishes social-ecological resilience because social capital is a key factor that helps agricultural or resource-dependent communities manage risk and adapt to changes and stressors. We consider the policy implications of our findings in the context of scientific and industry efforts to minimize social harm, promote economic vitality, and improve the sustainability of hydropower as a form of renewable energy. 2 currently home to approximately half of the world's large dams, it adds dozens of new ones to its portfolio every year for irrigation, river navigation, flood control, and, most significantly, hydropower generation. Most of these dams involve large-scale population displacement, and China's Ministry of Water Resources acknowledges that at least 15 million people have been involuntarily resettled over the past several decades alone (Yao 2004).When dams are built and reservoirs fill behind them, they displace the people who live there, inundating farmland and changing people's lives and livelihoods. A growing body of evidence has shown that the social effects of displacement can last for generations as people cope with the consequences for their household income, their access to land and other resources, their community identities, and their physical and mental well-being. As the WCD concluded in its seminal report, these effects are "spatially significant, locally disruptive, lasting, and often irreversible" (WCD 2000: 102), with the potential to undermine the long-term sustainability of the hydropower sector worldwide. Despite global assessments by the WCD and similar organizations, policymakers often make decisions without systematic information about the soci...