Nature Climate Change, Published online: 22 September 2025; doi:10.1038/s41558-025-02447-2
C40 is a global network of mayors united in a commitment to climate change action. Since its inception in 2005, C40 has grown to include nearly 100 of the world’s cities, maintaining high standards that focus on inclusivity, collaboration and science-based approaches to combat climate change. We interviewed members of the C40 organization, including mayors of its member cities, to ask about the history, success and challenges of C40, and their plans for future action.