As a nation of immigrants, the United States has long accepted that citizens who identify with an ancestral homeland may hold dual loyalties; yet Americans have at times regarded the persistence of foreign ties with suspicion, seeing them as a sign of potential disloyalty and a threat to national security. This book examines this contradiction in the realm of American policy making, ultimately concluding that the relationship between diaspora groups and the government can greatly affect foreign policy. This relationship is not unidirectional—as much as immigrants make an effort to shape foreign policy, government legislators and administrators also seek to enlist them in furthering American interests. From Israel to Cuba and from Ireland to Iraq, case studies illustrate how potential or ongoing conflicts raise the stakes for successful policy outcomes. Chapters provide historical and sociological context, gauging the influence of diasporas based on population size and length of time settled in the United States, geographic concentration, access to resources from their own members or through other groups, and the nature of their involvement back in their homelands. The book brings a fresh perspective to a rarely discussed aspect of the design of US foreign policy and offers multiple insights into dynamics that may determine how the United States will engage other nations in future decades.