Chapter 15 of Earthopolis: A Biography of Our Urban Planetexplores the role of professional planners in redesigning cities to manage problems associated with their growth, thus making accelerated Urban Planetary growth possible. Managing and enhancing flows – within cities and beyond them – was central to this work. Partly this was about control of urban water, in rivers, storms, for drinking, and for waste through various systems of embankments. Management of flows of air, foot and vehicular traffic, commerce, and potentially revolutionary crowds were also main goals of their work. The chapter traces two planning traditions as they emerged and then merged – that of eighteenth-century sanitarians and sewer and embankment builders in Calcutta and London, and that of boulevard builders in the French tradition. The latter tradition climaxed in the work of Baron Haussmann in Paris, but his work influenced planners in Buenos Aires, Rio, Rabat, Cairo, and New Delhi among many other places. Attention to flow could also beget inequality and segregation, as planners like Haussmann rebuilt Paris above all to serve the rising bourgeoisie, not the city’s even larger industrial working class.