Over the past four decades, immigration to the United States has grown rapidly both in absolute numbers and as a percentage of the American population.  While the federal government has been largely responsible for the admission of immigrants and the enforcement of immigration laws, states and localities play a critical part in the integration of immigrants into communities.  As the magnitude and nature of immigration—and the challenges associated with it—have transformed the political and policy landscape, the roles of the federal government and the states have evolved, sparking both new cooperation and points of friction.  Pew examines the intersection of federal, state, and local immigration laws and policies.