Book excerpt: The international statuses of currencies shape a fundamental characteristic of the international monetary system, which has significant impacts on the world political economy by affecting the political as well as economic relationships among states. The study of international currencies has been long dominated largely by economists, however, with political economy research in this area quite underdeveloped. However, the 2008/9 global financial crisis, the subsequent European debt crisis and the recent active Chinese promotion of renminbi internationalization have spurred new and considerable interest among political economists on issues surrounding international currencies. Political economy study of international currencies has thus been gradually growing of late, and making notable progress. This study provides a comprehensive and systematic review of the literature on international currencies -- covering both political economy and economics -- with the primary aim of building a useful groundwork to help develop a better research framework for the political economy study of them. In particular, it discusses the international currency concept, the costs and benefits of international currency issuance, the determinants of currency internationalization, and the future prospects of the current dollar-centered international monetary system. This research in addition highlights a group of important issues that need further investigation by future political economy study of international currencies, by drawing special attention to the following issues: historical events, the political determinants of currency internationalization, government policy strategies, and the consequences of international currency choice.