This chapter relates the Human Resource Management (HRM) system to the project-oriented organization. It introduces a working model based on social system theory as theoretical lens. The working model serves the purpose of observing the HRM system for the project-oriented organization. Mayerhofer and Steyrer point to the advantages of analysing HRM with the lens of Social Systems Theory. The units of analysis are the context, the internal structures of the HRM system and possible relations between the system and its environment, whereas the latter are part of the internal structures. The time-related context includes the history of the HRM system and its future expectations, as well as the history of the project-oriented organization and its future expectations. The HRM system explicitly recognizes the existence of temporary projects in the project-oriented organization and adapts its HRM internal structures accordingly.