The Performance of the EU in International Institutions marks one of the first attempts to systematically analyse the subject. It focuses on the role of the EU in decision-making within international organizations and regimes as a major locus of global governance. The book unpacks the concept of EU performance into four core elements: effectiveness (goal achievement); efficiency (ratio between outputs accomplished and costs incurred); relevance (of the EU for its priority stakeholders); and financial/resource viability (the ability of the performing organization to raise the funds required). Based on the case studies herein, the findings presented in this book relate to the identified core elements of performance with a particular emphasis on the dimensions of ‘effectiveness’ and ‘relevance’. Most notably, the EU appears, on balance and over the past two decades, to have become much more relevant for its member states when acting within international institutions. The book highlights four particular factors explaining EU performance in international institutions: the status of relevant EU legislation and policies, the legal framework conditions including the relevant changes that the Lisbon Treaty has brought about, domestic EU politics, and the international context.This book was originally published as a special issue of the Journal of European Integration