International organizations (IOs), defi ned as intergovernmental entities based on a multilateral treaty and possessing a permanent secretariat, have always been of concern to scholars of International Relations (IR). Students of IR used to focus on the international system by analytically separating the international level from national domestic politics. International organizations were viewed as an outcome of a struggle between national governments; from this perspective, IOs were expected to change according to the changing national interests that were responsible for creating them. With the spread of institutionalist thinking in IR (fuelled by the end of the Cold War and efforts to strengthen regional integration), IOs are increasingly considered to be more than the mere instruments of their members. International Relations scholars have, for example, started to identify differential state preferences in order to permanently delegate certain competences to IOs (Abbott and Snidal 1998). Yet the consequences of intra-organizational variation in formal administrative structures or the informal behaviour of international civil servants, especially when it comes to the explanation of organizational policies, are largely still outside the focus of ‘standard’ IR.