Introduction: Fragmented multilateralism and international institutions: between complexities and challenges 1.‘Authentic’ multilateralism and the stigmatisation of ‘small circles’: China, India, and the contestation over institutional design 2. The United States and fragmented multilateralism: bookending a century of US ambivalence towards formal international organisations 3. Traditional multilateralism in the shadow of bilateralism: UN emanations in the international investment agreement regime 4. An informal mode for multilateral cooperation: assessing the European Union’s engagements with informal intergovernmental organisations (IIGOs) 5. Peace and security ad hoc coalitions: engagement of the Global South and the Global North 6. Formal frameworks, informal practices: how ASEAN navigates the crisis in multilateralism 7. The European Union and the crisis of multilateralism in an era of uncertainty and power politics 8. The untold story: informal intergovernmental organisations in Latin America Conclusion