The increasing role that NGOs play at different levels of legal relevance - from treaty-making to rule implementation, and from support to judges to aid delivery - calls for reconsideration of the international legal status of those organizations. This book shows that the degree of flexibility currently enjoyed by NGOs in fields as varied as human rights, the environment and the European Union development cooperation policy constitutes the best arena for all actors involved, with the consequences that the instances where more strict regulation of NGOs' participation is desirable are very limited. With each chapter focusing on a different modality of NGO participation in international affairs (from formalised legal statuses to informal ways of dealing with issues of international relevance), this book will be of great interest to academics specialised in international law, political scientists, international officials working for both international organisations and non-governmental organisations, and legal practitioners (legal counsels of international organisations, lawyers and judges).