The Immigration Act of 1965 was one of the most consequential laws ever passed in the United States and immigration policy continues to be one of the most contentious areas of American politics. As a "nation of immigrants," the United States has a long and complex history of immigration programs and controls which are deeply connected to the shape of American society today. This volume makes sense of the political history and the social impacts of immigration law, showing how legislation has reflected both domestic concerns and wider foreign policy. John S. W. Park examines how immigration law reforms have inspired radically different responses across all levels of government, from cooperation to outright disobedience, and how they continue to fracture broader political debates. He concludes with an overview of how significant, on-going challenges in our interconnected world, including "failed states" and climate change, will shape American migrations for many decades to come.