This study examines the impact of High Performance Work Systems (HPWS) on company and employee-level performance outcomes. At the company level, the study examines the outcomes of HPWS usage on innovation, productivity and turnover. The study uses data collected from 132 companies in Ireland who participated in a general manager (GM) and human resource (HR) manager survey conducted in 2006. This study shows that an extensive application of HPWS is associated with an increase in innovation, productivity and a reduction in voluntary turnover. At the employee level, the study examines employees’ perceptions of human resource management (HRM) practices and their impact on employee innovative work behaviour (IWB), organisational citizenship behaviour (OCB), and tenure intentions. Specifically, the study also measures whether employees’ perceptions of job demands mediate the relationship between employee perceptions of HRM practices and IWB, OCB and tenure intentions. Employee attitude surveys were conducted in five companies which took part in the General Manager/Human Resource Manager Survey in 2006. In total 220 employees were surveyed. In addition to employee surveys, interviews were carried out with HR managers or a relevant manager in the area of employee management in the five companies that participated at the employee level. Overall, employee-level findings suggest that positive employee perceptions of human resource management practices are associated with employee IWB, OCB and tenure intentions. Similarly, employee perceptions of human resource management practices have an indirect effect on employee outcomes, in particular IWB and organisational citizenship behaviour directed towards individuals (OCBI) via employee perceptions of job demands. This study uses cross-level inference (also known as the cross-level operator) to examine the impact of HPWS utilisation at company level on employee-level behavioural and attitudinal outcomes. Overall, cross-level findings suggest that greater use of HPWS is associated with positive employee perceptions of HRM practices and an increase in employee IWB, OCB and tenure intentions.