This book investigates the complex nature of urban systems, exploring how uncertainty plays a crucial role in understanding cities. Daniele Chiffi and Stefano Moroni develop a relational theory to examine cities as dynamic networks of interaction between people and objects, rather than as fixed structures. Chiffi and Moroni analyse how uncertainty affects urban planning, infrastructure and technological advancement, challenging conventional paradigms by demonstrating how uncertainty can spark innovation. They further assess how public authorities make decisions in complicated urban contexts, focusing on areas such as land use and building transformations. The book proposes a novel framework for understanding technological innovations in the city, emphasising that progress is not solely driven by economic factors, but also by societal preferences and underlying uncertainties.