This chapter provides insights into the concepts and theories behind human resource management (HRM) and international human resource management (IHRM), as well as exploring the various concepts that may affect the ways HRM is utilised by multinational enterprises (MNEs) and other forms of international operating firms. Additionally, it reviews and critically discusses the theoretical and empirical work that has been carried out to explain the differences in IHRM in domestic organisations (DEs) and MNEs, highlighting the importance of understanding these differences when looking at the relationship between HRM and performance. Given the increasing role of contextual factors in the field of HRM, this chapter addresses the relevance of the particular international business (IB) environment within the development and execution of HRM practices and policies.