This chapter provides an overview of the key concepts discussed in the subsequent chapters of this book. The book focuses on characteristics that make urban sustainability transitions distinct from domain-based transitions. It also focuses on experimentation and its role in urban sustainability transitions, and the politics of urban space, conflict and urban sustainability transitions. The book shows that "a combined approach of urban ecology and sustainability transitions can provide insights into the functionalist components of the city while addressing the social and political construction and meaning" of these relations and infrastructures. It offers a perspective on the extent to which different urban contexts open up or not the appropriate context of experimentation, and in those in which it happens, how experiments can lead to demonstrable sustainability improvements. It suggests that examining the politics of urban sustainability transitions will provide a fuller explanation of the ways solutions in cities are debated, adapted and hybridised.