To address this question, this project takes a Multi-Method Research approach that is suited to test and further develop principal-agent theory. We employ fuzzy-set Qualitative Comparative Analysis and fuzzy-set ideal type analysis for a systematic cross-case comparison and, subsequently, process-tracing for an in-depth study of selected international bureaucracies, each of which are analyzed for specific policies. We test our theoretical expectations on 27 international bureaucracies, where we gather data on four organizational characteristics: fragmentation, staffing rules, buffering, and permeability. The chosen approach will allow us to investigate necessary and sufficient conditions for the occurrence of agency slack, to identify underlying causal mechanisms, and to assess the plausibility of alternative explanations. The insights gained from the project will enable us to map different patterns of agency slack and explain under which organizational structures international bureaucracies act against their principals’ preferences. Showing how organizational structure matters by comparing different international bureaucracies will enrich principal-agent theory and help us bridge the gap between theoretical considerations and empirical work in the field.