The digital reconstruction of architectural and urban complexes, which were demolished, transformed, or have been only theoretically conceived, remaining “on paper,” is now a tool of considerable heuristic value, allowing to preserve, interpret, and create new images of cultural heritages that no longer exist in their original shape or never reached a material construction. The tools, methods, and techniques of representation (graphical analysis, two and three-dimensional modeling, animation, prototyping) should be carefully chosen, case by case, in order to interpret properly the basic data and create original interpretations, using as research sources and ideas not only the archival drawings and any surviving vestiges but also the autobiographical writings and the more inspired analysis developed by the architecture critics. The examination of several international case studies and also some experiences personally conducted highlights the different strategies used for the preservation of the memory of such heritage.