Sigfried Giedion’s Bauen in Frankreich (1928)1 is one of those books that posterity has come to rediscover as a decisive text in early modernist architectural theory, even though it received little attention in its own time. The book projects a dazzling view of the new industrial architecture, and it is itself one of the period’s most effective visual-rhetorical constructions, in which the graphic design of Moholy-Nagy juxtaposes Giedion’s forceful and prophetic statements to images of the new machine technology in order to convey a sense of an irresistible modernity. But it also takes us right into the heart of the philosophical claims of the modern movement by proposing a radical interpretation of space that brings together motifs from a discussion underway since the latter third of the nineteenth century, and by projecting a new view of the organic and the technological. In this it also draws out a set of consequences for social space that Giedion’s subsequent and more “official” work, Space, Time and Architecture (1941), will retract in order to mitigate any “avant-gardist” conclusions, above concerning the very existence of “architecture” itself.