Strategic human resource management researchers have strongly advocated a system perspective and provided considerable evidence that certain systems of human resource practices have a significant impact on individual and organizational performance. Yet, challenges of understanding the construct of human resource systems still remain in the literature. Specifically, few efforts have been made to explicate the internal fit in human resource systems referring to how the practices in human resource systems work together. For the purpose of clarifying human resource systems construct, we review the components of human resource systems and delineate how the parts of human resource systems work together to influence employee performance. Theoretical and empirical implications for future research are also discussed