Cities are large emitters of greenhouse gasses, but are also extremely vulnerable to climate change impacts. This unique position makes cities networks relevant in international discussions on mitigation, where they have over the past few months effectively created a new initiative to cut emissions, along with a credible emissions accounting and reporting protocol, a data repository, and a portal to share progress. At the same time that cities groups are advocating mitigation at the international level, groups within cities are proposing innovative adaptation ideas to address local level climate change impacts, including creative solutions to adapt the urban landscape to sea level rise.