This article demonstrates how the evolution of US social sciences during the Cold War influenced French attempts to develop Algeria economically and socially. During a violent war of decolonization, French researchers drew from social psychology to inform development policies. Studying political trends through the lens of cultural and psychological factors transformed older understandings of social classification. Rather than being conceived in primarily biological terms, racial difference was increasingly defined in relationship to economic capacities. The Constantine Plan, introduced in 1958, exemplified the intimate link between social planning and the postwar social sciences. The article then studies attempts to develop the Sahara, where planners sought to determine which races would be able to work in the harsh conditions of the desert. Arguing that social planning in Algeria was not merely a ‘colonial’ phenomena, this article shows how development reflected the broader shifts in thinking about the economy and social organization that marked the 1950s and 1960s.