What difference do nonstate actors in international relations (such as Greenpeace, Amnesty International, IBM, or organizations of scientists) make in world politics? How do cross-national links interact with the world of states? Who controls whom? This book answers these questions by investigating the impact of nonstate actors on foreign policy in several issue areas and in regions around the world. It argues that the impact of such nonstate actors will depend on the institutional structure of states as well as international regimes and organizations.