This introduction presents an overview of key concepts discussed in the subsequent chapters of this book. The book is organised in the threefold structure the problematic of retrofit; governing and organisation of urban retrofit; experiments, learning and urban retrofit through which significant aspects of our understanding of urban retrofit are developed. There are overspills across these themes but in each theme the chapters highlights distinctive parts of the overall retrofit argument. First it examines why retrofit is emerging as an important strategic issue for urban authorities and untangles the mix of economic, competitive, ecological and social pressures and drivers. Second it needs to understand how retrofit capacity and capability is currently being organised with what inclusions and exclusions. Third, to examine the ways in which retrofit is contested and disrupted in practice and how learning takes place about the limits and opportunities for retrofit under different assumptions and conditions.