This chapter examines the deployment of the Taylor and the REFA (Reichsausschβ für Arbeitszeitermittlung) systems as “German Taylor systems” in relation to changes in historical conditions. First, it considers the deployment of the Taylor system during and after World War I until 1924. In addition, the introduction of the Taylor and REFA systems during the relatively stable period of the 1920s is discussed. The social and economic backgrounds of the Taylor system diffusion, modification of the Taylor system into the REFA system, and the roles of rationalization science in implementing the REFA system are explored. Furthermore, the management functions of the REFA system and its influence on workers are examined and compared with those of the Taylor system. Based on these discussions, the introduction of the REFA system in major industrial sectors, such as the iron and steel, electrical engineering, machinery, mining, and chemical industries, is considered, and the overall conditions are elucidated. Through these discussions, changes in labor management will be clarified.