This talk compares two cases of research, advocacy, and preservation of modern built heritage in U.S. cities, drawing on our recent books Heroic: Concrete Architecture and the New Boston (2015) and Imagining the Modern: Architecture and Urbanism of the Pittsburgh Renaissance (2019). In Boston, the concrete buildings that transformed the city during the 1960s and 1970s were conceived with progressive-minded intentions by some of the world’s most influential designers, including Marcel Breuer, Le Corbusier, I. M. Pei, Henry Cobb, Araldo Cossutta, Gerhard Kallmann and Michael McKinnell, Paul Rudolph, Josep Lluís Sert, and The Architects Collaborative. In the same period, an ambitious program of urban revitalization transformed Pittsburgh and served as a model for the postwar renewal of other U.S. cities. Billed as the Pittsburgh Renaissance, this era of superlatives—the world’s first aluminum-clad building, the largest retractable dome, the tallest exposed steel structure—brought together powerful urban planning authorities, visionary mayors and business leaders, and architects and designers of international renown to address the social, economic, and environmental problems that confronted the postwar city. Today, when urban renewal-era buildings across the nation are under threat of demolition or insensitive renovation, these research efforts survey the intentions and aspirations of the period, explores what was built (and what was imagined), and asks what these histories might suggest for the future of U.S. cities.