The aim of this thesis is to identify the key roles of expatriates in a major Japanese MNE and factors influencing formation of their roles. It also examines to what extent expatriates have discretion in forming their roles. The thesis uses empirical data from 109 interviews and 5 years of action research (44 advisory board meetings and 144 Human Resource Management (HRM) workshops, 19 research sites in 9 countries and 17 additional meetings on specific topics) that enabled the researcher to carry out insightful and in-depth analysis with cross-national and multi-layer perspectives. The study applies organisational design theory to unveil the mechanisms of role formation, significantly expanding the understanding of these issues in Japanese business and the international business literature. The findings suggest that the process of role formation of expatriates can be explained by combining contingency theory and strategic choice theory in a framework that argues that the roles of expatriates are the result of a political process of organisational design (Child, 1997). This includes adaptation to the environment (Lawrence and Lorsch, 1967) but also the relationship between organisational agents and the environment in the process of strategic choice (Child, 1997). The major contribution of this study is to provide evidence that expatriates are not merely agents of HQs in international business as traditionally understood, but that their role is more complex and multifaceted. The study empirically identifies five key roles of expatriates – two more than previously identified in the literature – and unveils six contingency factors and two strategic choice factors influencing role formation. The thesis demonstrates that expatriates strategically select their roles, although internal and external factors can act either as enhancers or obstacles to their making of choices and role formation.