This second edition of GEO for Cities is an extension of the main GEO-6 report, presenting and explaining the findings of the United Nations Environmental Programme (UNEP) flagship environmental assessment in a way that helps city decision makers take clear action. Chapter 2 of this report examines how cities function and the challenges and barriers to action they face, as well as some opportunities for catalysing change. Chapter 3 then examines how the environmental challenges of today are affecting cities and how cities are contributing to these environmental issues. Chapter 4 examines the types of future cities that will help address the environmental, economic and social challenges we currently face. City decision makers may see themselves in the dimensions set out in the chapter, alongside areas where their cities could improve. Finally, chapter 5 explores the pathways that need to be followed to reach the vision of “ideal” cities that is presented in chapter 4.