The objective of this essay is to investigate the circulation of knowledge about rationalization in industrial management between 1910-30 in Sweden. It builds on and tries to fill a gap in previous scholarship on the topic of industrial relations and the “rationalization movement” in Sweden. This essay focuses on the industrial employers affiliated with the biggest Swedish industrial union; Sveriges Industriförbund, and how they understood, presented and shared their knowledge about rationalization with each other. Why did the conceptualization of rationalization change during the years in question, and how did this knowledge in transit adapt?  One key finding is that the idea of rationalization changed and came to mean more things, and include more things as the industries faced more social and political challenges from the workers movement. The language surrounding rationalization came to include more demands for cooperation, mutual understanding and more humane working conditions as time went on. Rationalization also tended to be more professionalized and specialized as time went on, as a response to a larger and more intricate industrial apparatus. Because of the need for more skilled engineers and white-collar staff, industrial employers started to advocate for sharing the knowledge about rationalization with their workers. By the end of the 1920’s the industrial employers also knew that mental stimulation, and a general knowledge about the work process was required both for the smooth functioning of the company, but also for the mental functioning of the worker.