We can no longer continue to build the city of tomorrow with an architectural logic that dictates one building = one use. The inherent permanence of architecture and buildings contrasts sharply with the fluidity of contemporary society. Built heritage cannot be treated as a consumer good because it ties up too much energy, resources, and time. To be truly sustainable, how can we adapt to this future obsolescence? How can we strive for a timeless architecture? Creating architecture as a completely reversible object risks producing an architecture without roots, without history, incapable of considering all the issues that must be addressed in the creative process. Following a symposium organized by the research group on the invention and evolution of forms and by the National School of Architecture of Brittany in 2020, this book opens two avenues of reflection explored by some fifteen authors, architects, and researchers. Form: What forms should architecture take if it aspires to endure beyond its program and current use? How to anchor a building to a site? What architectural and functional features should be proposed? And what construction methods should be adopted for structures and facades?