The book presents in-depth case studies of six cities in the USA and Germany and provides a comprehensive introduction to the principles of sustainability, discusses the key governance instruments relevant to urban sustainability, and delivers new empirical and theoretical material on their role in a sustainability transition. It concludes that despite the national-level differences, cities? experiences in both countries are similar. Political sustainability at the city level differs in several important ways from academic principles of sustainability. Finally, it proposes that sustainability-minded groups may be a key link to connect urban sustainability in practice to theoretical concepts.