This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book recognises the urgent need for new approaches to dealing with the systemic environmental, economic and social challenges facing an urbanising world. It discusses the developing and implementing the concept of regenerative urban development, first outlined in Murray Bookchin 2010 world future council report 'regenerative cities'. The central contradiction people currently face is this: humanity is building an urban future, yet urbanisation in its current form is threatening the very future of humanity and the natural world. The urban metabolism, which currently operates as an inefficient and wasteful linear input-output system, needs to be transformed into a resource-efficient and regenerative circular system. Urban ecology is the study of living organisms and their relationship to each other and their surroundings in an urban context. Urban ecology has also started to focus on the impacts of urban resource use on regional ecosystems.