How can urban testimonies of the 20th century be preserved as an "experiential whole" in the present and future? How should heritage conservation engage with the modern city? Nine case studies of European cities, ensembles, and settlements illustrate the challenging balance between preservation and design. The contributions come from historians, representatives from the fields of building research and inventory, practical heritage conservators, architects, and urban planners. What criteria play a role in the justification of heritage? In addition to physical preservation, spatial concepts—such as the urban planning guiding principle, the essential content of the city plan, or a consciously pursued flexibility in use—are becoming increasingly important. How can the value of testimony be maintained when urban political decisions, economic, social, or demographic factors come into play?.