As internationalization has become part of the raison d'être of universities worldwide, English-medium instruction (EMI) has emerged as an irresistible force in the higher education systems of many non-English speaking countries. In a manifestation of its commitment to internationalization, Japan has seen a dramatic increase in the number of EMI programs now in place at universities throughout the country. This paper looks closely at EMI in Japan's system of higher education through an examination of the existing literature and an assessment of government policies and university practices designed to internationalize the system. The different rationales motivating the various stakeholders (nation, university, and individual) are identified, and the internal and external factors that have led to the introduction of EMI into Japanese universities are discussed. Insofar as EMI is more than a mere linguistic change, it will have a huge impact both on education and research. This paper then raises significant ideological and practical issues associated with English in education as a tool of "academic imperialism" in the unique Japanese context. It also addresses the different practices and adaptations of EMI at Japan's "elite" and "mass" universities. Finally, the double meanings of "internationalization" through EMI programs is conceptualized with using the terms of "internationalization abroad" and "internationalization at home" through examining the framework of nationalistic and cosmopolitan dimensions. For the further study and implications for university practices, the author asserts the importance of developing language education policy not to serve English imperialism but to facilitate focused research by students with a critical perspective.