This chapter focuses on the findings from five case studies in which author studied the Human Resource Management (HRM) system in the context of mature project-oriented organizations. As a means of analysing HRM systems of project-oriented organizations, the case studies have been selected in such a way that they all present companies which possess a high maturity in managing projects. Relevant stakeholders of the HRM system are Project Portfolio Group, Project Management Office, line managers/expert pool managers, project managers, project owners and project personnel. All case study companies had more or less an explicit strategy to support project-orientation. Project personnel are recruited by the project within the organization or outside the organization, and assigned by the permanent organization to a project. The role of the project manager is often the first role to be assigned. The project manager is selected for a particular project in relation to his/her competencies.