At the close of the 2012 Urban Age conference in London, the urbanist and social theorist Richard Sennett argued that the tendency to build large-scale new cities and neighbourhoods is depriving us of the social and creative energies of traditional urban form – often referred to as cityness. He returns to this theme in this newspaper for the Urban Age conference in Rio de Janeiro by framing the debate on cities as a contrast between efficiency and sociability. This duality is at the heart of the investigation of the interrelationships between the social and the physical in cities, which since 2005 have shaped the explorations of the Urban Age programme at LSE Cities