ABSTRACT In the aftermath of the Great War, the new science of psychotechnics was enlisted in the construction of the democratic social order that emerged from the ruins of German authoritarianism, a key component of the fragile social compromise between capital and labor that was a foundation of the Weimar Republic. During the 1920s, representatives of this branch of social engineering promised to use science to conjure away the workplace conflicts that had wracked Wilhelmine Germany and to usher in a new era of social harmony and productivity. Advertised as modern, rational, and humane, psychotechnics became a cornerstone of the rationalization movement that, originating in America, swept Germany in the 1920s. This article, focusing on interactions between psychotechnicians and female switchboard operators, places the objectives and contradictions of this new science of the working self within the context of wider debates about Germany’s postwar economic and political restructuring as well as the proces...