Issues associated with state inability (or incapacity) to meet international commitments—and how to build such capacity—are now ubiquitous in the theorizing, practice and research agendas of international environmental cooperation. Yet “capacity” and “capacity building” remain under-specified at the conceptual level. They are neglected areas of empirical research, and generally unreflective in practice. International and national level policy-makers are struggling with questions about how best to enhance state, local and NGO capacities to meet international commitments. To illustrate the need for more conceptual attention and empirical research around issues of public sector capacity, the article presents a multi-dimensional understanding of public sector capacity and highlights programs that appear to be successfully building capacity in recipient countries and programs that seem to be unsuccessful. The article draws examples from multilateral assistance programs within regional marine pollution control regimes and from bilateral assistance programs associated with cleaning up radioactive legacies of the Cold War in post-communist states.