Performance management systems have traditionally been developed by organisations to help ensure that organisational goals and targets are met. However, performance management systems appear to promise more than they deliver. The complex nature of the performance system is in part due to the various components within the intended and actual performance management sub-systems (functioning as individual systems) that run within the overarching performance management system. Many organisations experience deviations from the intended system, where performance management has been perceived to be ironically underperforming and not meeting senior management’s expectations. Notably, the implementation of performance management is the responsibility of managers; more importantly, a key part of a frontline manager’s role is ensuring that frontline employees, who make up the majority of the organisation, are performing to meeting organisational goals. It is therefore important to understand how the overarching performance management system in an organisation (with its various sub-systems that have multiple components, and processes) is managed by frontline managers and how the behaviours of all managers influence the implementation of performance management. However, existing research has shown a lack of focus on the role of frontline managers in the implementation of performance management systems, despite plenty of research on the separate topics of frontline managers and performance management. This is surprising, given that frontline managers are responsible for overseeing most of the organisation’s day-to-day operations. Moreover, little is known about how frontline managers connect the intended performance management system, through components and processes developed by the human resources department and higher levels of management, with their employees’ performance. Frontline managers find ways outside the formal system to bridge the gap between intended and actual performance management systems in organisations. Despite being commonly termed ‘performance management systems’, performance management has not been studied using a systems theory lens – instead of the interaction between sub-systems that have various components and processes within a performance management system, performance management tends to be studied through its individual components and processes. As such, there is a lack of understanding regarding the interaction between formal and informal performance management systems. This thesis addresses these issues by using systems theory to illustrate the complex and dynamic nature of performance management in practice. The focus is on the perspective of frontline managers as the key actor in performance management in the context of the expectations and actions of other actors in the system. In doing so, this thesis examines the implementation process of the intended performance management system. The actual performance management system, as experienced by frontline employees, is the result of their respective frontline manager’s discretionary behaviour when implementing the intended system. An inductive case study approach is utilised in this thesis using qualitative data collected from two public sector organisations in Singapore. Although from two different sectors, PublicWorks and AdminInc (both are pseudonyms) share similarities in their performance management systems. Within each organisation, data were collected from at least two different departments and across the different levels of employees. At PublicWorks, the data were collected from three different departments and the HR department; at AdminInc, the data were collected from two different departments. This research design enabled the cross-case analysis of data, both within and between the organisations. The data were collected through semi-structured interviews and documentation. In total, 57 interviews were conducted across different levels of management (senior, middle, and frontline management), the HR department, and frontline employees. A key finding of this research is that frontline managers often sought to maintain agency in the process using their discretion to balance meeting the demands and expectations of those both above and below them. Within the actual performance management systems, frontline managers were concurrently using the formal performance management system and informal performance management system to show their conformity with the intended performance management system and also to effectively manage the performance of their employees. They implemented the intended performance management system using minimalist compliance through the formal performance management system. The frontline managers’ apparent compliance with the intended system were through the implementation of the compulsory components through the formal performance management system aimed to keep higher levels of management and the HR department satisfied that they were executing their responsibilities. However, the design of the intended PM system did not allow for the frontline managers to appropriately manage the expectations of their employees. As such, their actions were not ad hoc, but were in effect set up using the developed, parallel informal performance management system with its own rules and internal consistency to manage the expectations of their frontline employees. A key feature of their actions was to maintain flexibility to manage their work units through their use of the formal and informal performance management systems. This study provides a more nuanced picture of frontline managers in action, implementing performance management to comply with organisational requirements and also ensuring they maintain flexibility in how they operate to meet operational goals and keep their staff on board and favouring informal styles of management wherever possible.