The chapter delves into the intricate relationship between urban and industrial metabolism, shedding light on the symbiotic interactions that occur between these two systems. This chapter aims at introducing the innate connections between urban processes and industrial processes. These connections have been widely studied in literature and are usually compared with human and biological phenomena. In that sense, in this chapter the concept of symbiosis between urban and industrial metabolism is discussed, as a way to contextualise and localise the contribution of the solutions presented in the following chapters. Overall, the chapter highlights the significance of understanding and optimizing the flows within urban systems for a more sustainable future, and thus places the empirical studies in the book section on urban eco-industrial development in a wider context.