The emergence of the Art Nouveau (late 19th century decorative style) was a revolution, in the sense of abandoning the historic architectural styles. The understanding of the artistic and historic laws of architectural development of the 20th century is indispensable for the knowledge of the new development trends of the beginning of the century. The follow-up of the architectural development of prominent creative personalities, of architectural trends and theories of the 20 the century, is completed by references to the development of modern architecture in the inter-war period, to the architecture of traditionalism, and examples of world architecture after World War II.