The course examines the architecture of the twentieth century, in Europe and in the United States, highlighting the different modernities of the twentieth century: that linked to the avant-gardes but also that formed by the interweaving of relationships between regional traditions and new languages. The reforming policies of housing and urban planning and the importance of the emergence of reinforced concrete will also be analyzed. The course also deals with the crisis of the Modern Movement, to the point of mentioning the frontier themes of the last decade of the century.