The C40 World Mayors Summit 2025, co-hosted by the Mayor of London and C40 Cities Co-Chair Sadiq Khan and the Mayor of Rio de Janeiro Eduardo Paes, brings together mayors from nearly 100 C40 cities, alongside business leaders, philanthropists, investors, academics, and civil society. 

This year’s Summit will kick off the COP30 Local Leaders Forum, co-hosted by Bloomberg Philanthropies and the COP30 Presidency. The Forum puts local leadership at the heart of global negotiations, showcasing scalable city-led solutions and ensuring local priorities shape the outcomes of COP30. 

Taking place from 3-5 November in Rio de Janeiro, just days before COP30 in Belém, the Summit marks a critical moment for city-led climate action. Building on two decades of C40 Cities leadership, it will showcase innovative solutions from cities worldwide, demonstrate what’s possible through delivery-focused collaboration, and build momentum ahead of COP30.