This thesis explores the question of whether Performance Management Systems (PMS) contribute to the managing of Executive Agencies (EAs). Exploring this question empirically in the context of the Jamaican public sector, it develops a realist methodology with methods, which are applied to the study of four Jamaican Executive Agencies (JEAs). Primary research conducted in 2011 through semi-structured interviews is combined with secondary research that considers both official government and unofficial resources such as reports (official) and newspapers (unofficial). The thesis is one of very few studies to focus on JEAs, one of only two studies to explore PMS in JEAs, and the first to make a focus on PMS in JEAs the primary object of study. It therefore contributes to a very limited literature, which is, therefore, both a strength of the thesis insofar as it breaks new ground, and also a challenge. It is a challenge because the lack of available literature on JEAs with which to relate. In order to address this lack, drawing on Historical Institutionalism (HI), Path Dependency (PD) and Policy Transfer theories, it argues that it is reasonable to draw on British literature owing to the historical influences of Britain on Jamaica, their institutional and constitutional contexts and, particularly, because the agencification of the Jamaican public sector has been based on the British Next Steps Model. From reviewing the British literature an Integrative Conceptual Framework (ICF) is developed. This framework incorporates those factors deemed as critical to the development of PMS in the organisational performance management literature, (that is, both management and public management), in order to harness the structural, procedural, situational and behavioural aspects discussed in the existing literature into a single framework. The ICF is at the heart of the thesis because it influences the methods used in conducting the primary research, and the presentation of research findings. It is therefore a major contribution of the thesis, and it is recommended that this framework could be applied in other contexts (e.g. in the private sector) and locations (e.g. in countries other than Jamaica) to analyse the use of PMS for managing. By triangulating the primary research findings with secondary data, that is, existing literature on the four case studies, the ICF is applied to generate a longitudinal aspect to the study. It is also found that PMS do contribute to managing JEAs, and that the use of PMS in JEAs has evolved positively over time for managing JEAs. The research findings discuss how PMS contributes to managing the four JEAs in terms of the different components of the ICF. Based on this, the study is able to add to existing academic literature, and make recommendations to practitioners. The contribution of this thesis to literature therefore incorporates both a conceptual and theoretical aspect, and also has a practical element. Both of these, it claims, could form the basis for further research.