The concept of smart cities holds environmental promises: that digital technologies will reduce carbon emissions, air pollution and waste, and help address climate change. Drawing on academic scholarship and two case studies from Manchester and Helsinki, this timely and accessible book examines what happens when these promises are broken, as they prioritise technological innovation rather than environmental care. The book reveals that smart cities’ vision of sustainable digital future obfuscates the environmental harms and social injustices that digitisation inflicts. The framework of “broken promises”, coined by the authors, centres environmental questions in analysing imaginaries and practices of smart cities. This is a must read for anyone interested in the connections between digital technologies and environment justice.