The United Nations and other international institutions are under severe strain, struggling to adapt to dramatic shifts in U.S. policy, surging geopolitical competition, North-South tensions, and destabilizing challenges from climate change to disruptive technologies. This moment of crisis, however, also presents opportunities for institutional reform. What might be done to make existing multilateral bodies more effective and legitimate, as well as resilient to future shocks? What new informal coalitions might be forged, including among middle powers, to advance collective responses to shared challenges?