In recent decades, there has been a steady increase in the number of international Organizations (IOs). At varying levels states have surrendered some authority to IOs, giving them different levels of institutional empowerment. While in the EU, IMF and World Bank there has been a steadily extension of their competences, in the GATT/WTO-Secretariat, NATO and WHO the degree of delegated authority has remained constant. How can we explain these different degrees of authority granted to IOs and their evolution over time? We argue that institutional empowerment is a function of temporal dynamics, the degree of cohesion among principals, and the institutional design of the delegation contract. On the theoretical side, the aim of the proposed interdisciplinary project is to produce theory-driven knowledge by developing a model of power delegation to IOs that integrates a temporal dimension into the principal-agent approach. This will be done by resorting to four different disciplines: political science, economics, law, and organizational sociology. On the empirical side, the main novelty of the project consists in adopting a comparative research design and a longitudinal perspective. We will analyse the institutional empowerment of six different IOs (EC/EU, GATT/WTO, IMF, WHO, UNESCO, and World Bank) over a period of 65 years (1950-2015). Given the aim and scope of this research, the project is to be regarded as theory-building and hypothesis-testing research. It will be based on extensive qualitative work conducted in the archives of these four IOs as well as on elite interviews with national and international officials. With this project we will gain new insights into the following fields: consequences of power delegation to IOs; temporal dimension of the interaction between states and IOs; preference formation of states; comparison of different types of IOs. This will allow us to answer the broader and more general question of the conditions under which IOs can operate as independent actors in world politics and to advance theoretical insights and empirical research in International Relations.