Recent trends in the historiography of international organizations are occupied with tracing their historical impact on national contexts. There is, however, no consensus on how to conduct this type of analysis methodologically. This article examines the methodological challenges arising from this type of research. While a great deal of inspiration can be gathered from contemporary impact assessment studies, substantial conceptual and theoretical development is needed to make the idea of "impact" operational and feasible in historical studies. It is, we argue, through the focus on impact levels, space, and movement that the idea of tracing the historical impact of international organizations becomes a promising research agenda.