While formal decision power in most international organisations rests with the member states, the member states often delegate the preparation of decisions to international secretariats. To prepare decisions, secretariats normally gather and analyse information. They subsequently provide the member states with an assessment, which lowers the uncertainty about the payoffs of alternative courses of action. In the process of preparing decisions, however, secretariats accumulate an information surplus over the member states, which they can abuse to further their own interests. This article argues that, to counter this classical agency problem, the member states invest in domestic shadow bureaucracies to lower informational asymmetries. Shadow bureaucracies are, however, very costly. Only member states with significant interests in a specific policy area will therefore make such investment. This gives them disproportionate control over international secretariats and thereby policy outcomes in international organisations. This article uses insights from the planning process of UN peacekeeping operations to illustrate the argument.