Twentieth-century architecture stands as an imperative realm of experimentation, within which the architecture of the Modern Movement emerged from 1900 to 1940 with shapes, features, and materials completely different from pre-industrial buildings, rejecting traditional construction practices, techniques, and materials. Its key design concepts include (i) the “Form Follows Function” principle, establishing a strict relationship between building aesthetics and function, favoring min-imalism, balanced composition, and visible materials; (ii) the creation of comfortable and healthy buildings, with natural light and ventilation through windows, biophilia, and spacious rooms; and (iii) advancements in engineering, facilitating novel design possibilities (e.g., metal-framed curtain walls, complex windows) and the manufacture of mass-produced materials (e.g., glass, steel, rein-forced concrete, plywood, Masonite, and cast iron). These criteria directly influence energy effi-ciency and human comfort. Nevertheless, technical problems have emerged due to inadequate com-prehension of the long-term performances of these experimentations, leading to deterioration and aging. This research provides a complete overview of the energy and climatic performances of Mod-ern Architecture, discussing building physics implications of the key design principles through sev-eral case studies.