9/11 served as a critical turning point in immigration law and policy in the United States. Possibly no other single event has done more to drive the political and legal-immigration reform debate in the United States this century. Since 9/11, the U.S. shares of immigrants, tourists, and international students have seen significant declines, and—as this paper documents—substantial portions of these declines trace directly to policy actions taken in response to the relatively slight threat of terrorism.