The ecological transition of cities is crucial for the ecological transition of the entire world. This transition goes through the transformation of the current linear urban metabolism into a circular metabolism that mimics the functioning of ecosystems. A metabolism aiming to the minimisation of material inputs (products, water, food) in order to minimise both the withdrawal of resources from the environment and waste production. This goal can be achieved by adopting the principles of the circular economy, maximising the use of renewable sources and energy efficiency, and redesigning urban services, such as mobility and water-and-waste cycles. In order to bring about this transformation, it is not enough to work on technologies and techniques because citizens’ behaviour, lifestyles and cultural values are affected. Furthermore, treating the city as a living organism, i.e., as a complex system, requires an appropriate design and governance method underpinned by a systemic vision.