International institutions, from the WTO to the UN Security Council, face mounting legitimacy challenges. Reforms promising greater procedural fairness are frequently proposed as solutions, but do they actually work? ‘After Reform’ provides the first systematic empirical answer to this question. Drawing on an original dataset of more than 9,500 legitimacy statements made by member states across three major institutions, Vegard H. Tørstad evaluates how procedural-fairness reforms shape states' perceptions of institutional legitimacy over time. Through in-depth case studies of participation reform in the UNFCCC climate negotiations, impartiality reform in GATT/WTO dispute settlement, and transparency reform in the UN Security Council, this book shows that reform effects are real but uneven — and identifies the conditions under which reforms are most likely to succeed. With multilateralism under unprecedented strain, ‘After Reform’ offers acutely timely new theoretical insights and concrete policy lessons for how to design international cooperation.