Transnational advocacy scholarship has illustrated the power of activist networks in overturning Cold War logics; facilitating disarmament and weapons control; tackling climate change; and promoting human rights. Since the 1990s, scholars have demonstrated that non-state actors can shape international outcomes, including through boycotts, persuasion, and information politics. Given the rich research agenda that these scholars set out, what have we learned in the last 20 years? And how can transnational advocacy scholarship help us understand larger trends in international relations? This forum brings together leading scholars of transnational advocacy to unpack the key debates in three areas: 1) external challenges, especially shrinking civic space worldwide; 2) internal challenges to transnational advocacy networks; and 3) the challenges and opportunities afforded by implementing international norms and international law at the domestic level. The forum brings together nine authors who have studied advocacy in Brazil, Russia, India, China, South Africa, Liberia, Côte d'Ivoire, Bolivia, Guatemala, United States, Australia, Germany, the United Kingdom and a host of other countries across a wide range of issue areas. These scholars use a range of methods from qualitative to quantitative studies of advocacy. Collectively we illustrate how transnational advocacy matters for IR and chart a future research agenda.