© 2017 John Wiley & Sons, Inc. All rights reserved. This chapter assesses three aspects of American foreign relations during the long Gilded Age and Progressive Era. First, it examines the role of the United States as an international police power within the Western hemisphere, in America's colonies, and along the US-Mexican border. Second, it characterizes the period as an age of globalization and greater interconnectedness, leading to new transnational social movements. Third, it investigates the arguments about the United States entering World War I and the postwar ratification of the Treaty of Versailles, paying particular attention to historiographical debates about the legacies of President Woodrow Wilson. It concludes with some observations about directions for future research on the United States in the world during the Gilded Age and Progressive Era.