The concept of trapped populations was introduced in a 2011 Foresight Report by the UK Government Office for Science. Trapped populations are the most vulnerable to climate and environmental change given extremely low levels of economic, social, and political resources. It is precisely this vulnerability that impedes the capacity to adapt by migrating, which entails considerable costs. That the most vulnerable to climate and environmental change are trapped in place raises concerns about the potential for large-scale humanitarian emergencies. Given these high stakes, it is surprising that research has yet to operationalize the concept of trapped populations to guide empirical efforts to identify those most at risk of being trapped in place and intervene accordingly. This paper fills this gap by providing the first operational definition of and a corresponding set of empirical steps to identify trapped populations that can be adapted and used by researchers, policy makers, and practitioners.