Many problems confronting today’s societies are transnational in character, leading states to increasingly rely on international organizations (IOs) for policy solutions. Yet the performance of IOs varies extensively. Apart from reviewing literature and conceptualizing IO performance, we introduce a taxonomy of five dimensions of policy output amenable to empirical measurement: policy volume, policy type, policy instrument, policy target, and policy orientation. Each dimension represents an issue of theoretical and empirical contention in existing scholarship. We conclude the paper by highlighting the implications of IO performance for effectiveness and legitimacy in global governance. Unless IOs are capable of developing and adopting new policy, they will be unable to solve the problems that motivated their creation. In addition, the performance of IOs is likely to have a bearing on their legitimacy in the eyes of citizens. Only IOs that deliver are likely to sustain popular support in the long run.
