This study investigates the constraints and success factors in the implementation of the third performance management system (PMS) for the Namibian public service from 2006 to 2014. It was purported to be implemented in 2006. However, various government publications reported that its implementation process was poor or slow. The study also made a contribution to the discussions regarding individual performance agreements by politicians. The review of the existing literature revealed that at the time of this study no academic research was conducted in the Namibian public service considering the PMS implementation process in totality. Furthermore, the conditions or factors of an effective policy and performance management system implementation which had been identified helped the researcher to decide on the focus of the study. Methodologically, the study uses an implementation research design which focused on process evaluation using the mixed method approach. During phase one, data was collected using a diagnostic tool to determine the status of the PMS implementation. The results of phase one guided the interviews conducted during phase two that provided an in-depth understanding of the phenomenon under investigation. A purposive sampling method was applied in selecting nineteen respondents who participated in this study. Documentary sources were used during all the phases of the study. The main findings of the study are: notable achievements in terms of the PMS design and its implementation, with four Offices, Ministries and Agencies (OMAs) and Regional Councils (RCs) being identified as most successful at the time of the study. Internal leadership commitment proved to be the main success factor. However, the PMS was not implemented fully because it did not meet the requirements of an effective one. The study recommends to establish the PMS unit in each OMA and RC, integrate the PMS with all aspects of human resources, simplify the PMS forms, formulate a PMS policy for Namibian politicians, apply the templates and implementation modalities of an individual performance agreement of political executives, formulate a social contract for the constituency councilors in the Government of the Republic of Namibia, and introduce a Constituency Development Budget (CDB) to support the implementation of the social contract. / Public Administration / D.P.A.