This chapter introduces the primary challenges urban areas are currently facing, regarding both environmental and ecological issues. It outlines the impacts of climate change (CC) on cities and their inhabitants and provides examples of nature-based adaptation solutions for the building scale and for open spaces. These topics are addressed in connection to the most relevant Sustainable Development Goal and other international environmental goals, from a design and planning perspective. Moreover, the chapter presents the structure of the book Nature-Based Cities, which aims to address the rising urban complexity by proposing approaches, methodologies, and tools to design Nature-based Solutions (NbS) for climate change adaptation.