Modern cities exist and function because of the highly developed systems which underlie them, ensuring that electricity, gas, heating, clean water and so on are moved efficiently from provider to user, and that waste is removed. Technical networks are the bedrock of urban development, physically and metaphorically. The services they provide are a precondition for basic standards of living, economic growth and environmental protection in and beyond the city. Comprising not just physical artefacts, such as power plants or sewers, but also organizational structures, institutional arrangements and socio-cultural meanings, these urban infrastructures represent complex socio-technical systems serving multiple purposes. Once established, they generally possess a high degree of path dependency; that is, by virtue of their physical embeddedness in urban (sub-)structures and their reliance on powerful regulatory and economic interests, they tend to be resistant to change. Since the 1980s, however, urban infrastructures have come under increasing pressures to adapt. Firstly, the political economy of socio-technical systems has diversified hugely following trends towards the liberalization, privatization and commercialization of utility services. Secondly, the socio-technical configuration of urban infrastructures is altering subtly but distinctly with the emergence of new, smart technologies, capable of providing more efficient services tailored to specific locations or user-groups. Thirdly, stricter and more ambitious environmental regulation in industrialized countries is providing a powerful driver for more resource-efficient and low-pollution forms of service provision and use. Overall, these forces for change are challenging the conventional logic of ‘build and supply’, and generating new ways of making utility services more environmentally, socially and economically sustainable.