After almost two decades of unprecedented progress in multilateral cooperation, 2025 sees global tax governance teetering on the brink of fragmentation. Both of the OECD’s ‘two pillars’ have broken new ground, but there are doubts that Pillar One, which would have provided a multilateral solution to the taxation of the digital economy, will come into effect. Meanwhile, negotiations at the UN for a new Framework Convention on International Tax Cooperation have highlighted sharp – possibly insurmountable – disagreements between global North and South. Fiscal pressures in all parts of the world are prompting renewed interest attention to wealth taxes and global solidarity levies, but for these to benefit the global South, they too would require multilateral cooperation. This policy brief draws on research from the International Centre for Tax and Development (UK) and the National Institute for Public Finance and Policy (India) on the politics of global tax cooperation and the needs and experiences of lower-income countries. Since the T20 Brazil communiqué outlined a vision for the future of global tax cooperation, its outlook has deteriorated. Now more than ever, the G20 must build on its legacy as a driver of progress in global tax governance, and demonstrate leadership in two priority areas: (1) supporting constructive outcomes from current negotiations at the UN; and (2) championing new areas of cooperation including taxing the wealthy and climate-related taxation.