Comparing non-governmental organizations (NGOs) in the United Nations and the European Union across a range of different issue areas, this volume examines how the choice of venue and institution affects the strategies of NGOs. Despite significant differences with respect to their scope, membership as well as their institutional rules, the authors find that the UN and the EU have surprisingly similar effects on civil society organizations and regulate access in such a way that it significantly constrains the agency of NGOs. Highlights include: A comprehensive outline of the volume's main research questions, situated within the existing literature on the topic Eight case studies of NGO involvement in the UN and the EU across a range of different areas, including human rights, the environment, socio-economic and security issues A theoretically grounded summary of case study findings, challenging the findings of previous studies regarding the power of NGOs A discussion of the finding's implications for the broader literature, as well as for studies relating to the EU and the UN in particular Transnational Activism in the UN and the EU will be of interest to students and scholars of International Relations, European Studies, and Global Politics. Jutta Joachim is Associate Professor of Political Science at the University of Hannover, Germany. Birgit Locher is a Research Fellow at the Institute of Political Science at the University of Tubingen, Germany.