Overview Today, a key challenge for policy and decision makers globally is how best to develop the knowledge and capacity to use resources more sustainably. Governments in the UK and across the world are therefore introducing increasingly challenging targets to reduce the impact we have on our environment, looking to issues such as the use of renewable energies, waste reduction and limits to carbon emissions. However, in what is an increasingly urbanised world, 'piecemeal' change cannot equip cities, as major foci of global population, to rise to the challenges of climate change. What is needed is a new approach, based on futures thinking, which embeds the ideas of ecological and social resilience into the very fabric of the built environment of cities. Set in this wider context, the ambition of 'retrofitting' existing cities has therefore gained increasing prominence within research and policy agendas in recent years as Sir David King notes in the foreword to this book (see also Dixon et al., 2014, and Hodson and Marvin, 2016). Whilst cities are seen as the source of many environmental and resource depletion problems, they are also recognised as centres of major population which offer not only huge potential opportunities in 'scaling up' technological responses to climate change, but also to act as 'hubs' of innovative social practice and learning. However, city level action requires a change in thinking, and rapid intensification of mitigation and adaptation responses, not only in response to climate change, but also to the allied threat of environmental degradation. What is required at city level therefore is a much more coordinated , planned and strategic approach so that cities can transition to a sustainable future over the next 30-40 years. The notion of urban or city-wide 'retrofitting' is anchored in the literal meaning of 'adding (a component or accessory) to something that did not have it when manufactured'