Based on discussions regarding changes in business management during the Weimar Republic in Part III, Part IV analyses business management in the Nazi period. Two research topics, the REFA system implementation and the Ford system deployment, are examined. This chapter considers the deployment of the REFA system by the strong involvement of the Nazi state. First, it explores the expansion of REFA activity and examines the progress of implementing and diffusion of the REFA system in major industrial sectors emphasized by the state for expanding munition production as well as the general conditions. The differences in the implementation of the REFA system between industries are discussed, and changes in labor management are clarified. Based on these examinations, the characteristics and significance of the diffusion of the REFA system supported by the Nazi policy are elucidated.