The chapter argue cities are instead increasingly involved in potentially transformative efforts to retrofit not only their built environments but also global environmental governance more in general. City networks have grown exponentially in numbers and membership and have progressively carved a more extensive role in environmental governance. Organizations such as ICLEI have made extensive efforts in this direction since the 1990, as with the Cities for Climate Protection (CCP) Campaign launched by ICLEI with the aim of gathering a coalition of local governments sufficient to account for at least 10 per cent of the global Green House Gas (GHGs) emissions. In recent years the Climate Leadership Group (C40) has fast emerged amongst peers as one of the most dynamic and proactive city networks in contemporary global environmental governance. Most metropolitan mayors, both in the West or in the Global South, can today display sets of powers that allow them some substantial retrofitting competence to tackle climate change.