This PhD examined the built production and activities of Belgium's two largest twentieth-century Belgian property developers: Jean-Florian Collin (1904-1985), founder of Etrimo (1935-1970), and François Amelinckx (1898-1975), founder of Amelinckx NV (1938-1985). These housing developers realized more than 70,000 apartments – housing more than 200,000 people – a large-scale production had never been studied systematically, nor was it aligned with the dominant anti-urban agenda that has been attributed to Belgian national housing policies. This research studies this production as the result of the "space" developers actively tried to claim for their development practices and the "space" given to them by society. It thus analyzes this commercial housing production as a mirror for the urban, architectural, economic, and political conditions in which it was realized. By examining the reciprocal relationship between the activities of Collin and Amelinckx and the social conditions in which they operated, this PhD evaluated the research hypothesis how society gets the kind of project development it deserves (or sets the conditions for) as a consequence of the type of actions it enabled and rewarded. Such an analysis contains important insights into the selection of the dominant model of twentieth-century project development in Belgium, and how project developers can take up a more productive role in housing the city.