Departing from Storper’s (2013) notion of a ‘genius of cities’ but extending the concept from agglomeration economies to inter-city networks and the built environment as foundations of cities’ genius, I argue that cities’ genius is Janus-faced. My contention is that cities’ specific environments not only breed all the ‘good’ innovations that drive innovation and growth but they also generate the ‘bad’ ones, which allow for the development of the means of exploitation. Cities are, as a result of their very properties, key places for the organisation of uneven development.