Somewhere between 1910 and 1970, architecture changed. Now that modern architecture has become familiar, sometimes celebrated and sometimes vilified, it's hard to imagine how novel it once seemed. Expensive buildings were transformed from ornamental fancies that referred to the classical and medieval pasts into strikingly plain reflections of new materials, functions, and technologies. Modern architecture promised the transformation of cities from overcrowded conurbations characterized by packed slums and dirty industries to spacious realms of generous housing and clean mechanized production set in parkland. At certain times and in certain cultures, it stood for the liberation of the future from the past. This very short introduction explores the technical innovations that opened up the cultural and intellectual opportunities for modern architecture to happen. Adam Sharr shows how.