My dissertation, “Cosmopolitan Medicine Nationalized: the Making of Japanese State-Empire and Overseas Physicians in a Global World,” examines the movement of Japanese physicians across Asia and the globe in the late nineteenth and first half of the twentieth centuries. By showing how doctors migrated to enhance their opportunities for career success, this study investigates the historical emergence of a cosmopolitan medical profession in Japan, its colonies, and other countries. At the same time, the globalization of the medical profession imposed a perplexing challenge to the sovereignty of modern states and empires, because licensing power and border control came to be regarded as essential components of modern state sovereignty in the early twentieth century. As self-proclaimed modern states, both Japan and the countries receiving Japanese physicians sought to impose more stringent regulations on foreign-trained doctors. I argue that this endeavor not only furthered the state’s control over both the medical profession and immigration, but also built an institutional infrastructure allowing for the evaluation of foreign diplomas and licenses. This eventually paved the way for the worldwide migration of medical workers from the second half of the twentieth century onward. Accordingly, this research elucidates a three-fold history: a national history of Japan’s modern state formation, an East Asian history of the Empire of Japan as a space of social mobility, and a world history of the development of physicians becoming state-sanctioned and yet internationally mobile professionals. My dissertation is organized chronologically and thematically in four parts. The first chapter investigates the evaluation of foreign-trained doctors in Meiji Japan and the countries receiving Japanese physicians, since it posed a problem for the local authorities and licensing system, as it was hard to determine whether a foreign certificate was real and the equivalent of their own. The second chapter explores how Korea and China, countries without any regulation of medical qualification, became lands of opportunity for Japanese practitioners who struggled within the increasingly competitive medical market at the turn of the twentieth century. Chapter three discusses how overseas Japanese physicians’ qualifications and capabilities were called into question when the rise of Japan as an imperial power caused great alarm to the receiving countries. The last chapter illustrates the gaps between the medical certification system in Japan and the sub-systems in Japan’s colonies. It also elucidates how the institutional discrepancies enabled colonial Taiwanese physicians to improve their inferior civic status and maximize chances for career advancement by moving to the empire’s other territories. I consider this research as not only a national history of Japan’s legitimation and demarcation of its state and empire but also an international history of the genesis of medicine as an internationally mobile profession.