This article introduces, summarizes and contextualizes the key questions and findings of a special issue of Global Policy on the resourcing of international organizations (IOs). The article sets out trends in the financial resources available to IOs; discusses their organizational consequences; and highlights analytical implications for the study of IOs. We discuss resource diversification associated with growing complexity of the origins and types of funding available to IOs; the importance of non-state actors in IO funding; and contestation over the classification of resources. Resource diversification encourages organizational differentiation, manifested in major shifts in resource-related actor constellations and their impact on the autonomy of IOs; adjustments to budgeting procedures; and functional differentiation within IOs and the emergence of new types of IOs that are partly driven by resourcing. These observations invite an analytical perspective in the study of IOs that pays systematic attention to the administrative governance dimension of IOs; the entrepreneurial character of many IOs; and organizational fields as a focus of analysis. Read together, the 11 contributions to the special issue underline that paying attention to their resourcing can advance our understanding of IOs.