Foreign judges sit on domestic courts in over 50 jurisdictions across the world. The practice raises underexplored questions about the significance of foreignness and mobility to the judicial role. This chapter draws on the contributions to The Cambridge Handbook of Foreign Judges on Domestic Courts to set out a framework for analysing the phenomenon of foreign judging and its legitimacy and effectiveness. Drawing on various incidents of foreign judging, it disaggregates five rationales for the use of foreign judges on domestic courts: necessity, institution building, distance, expertise and reputation. It identifies size, the domestic legal system, and the degree of international involvement as factors that make some jurisdictions more receptive than others to foreign judges. The chapter canvasses the implications of foreign judging for the identity and role of the judge, judicial independence and accountability, and adjudication and the development of the law. The experiences of jurisdictions across the globe suggest that foreign judging is a diverse phenomenon which will continue to evolve in contemporary conditions of globalisation.