The U.S.-Mexico border is one of the busiest in the world, with hundreds of thousands of vehicles and pedestrians–and hundreds of millions of dollars in trade—crossing legally through ports of entry each day. In addition, the ports of entry receive some of the asylum seekers and other migrants who are seeking to enter the United States. How have policies, procedures, and operations around would-be migrants evolved, in particular as migration to the border has increased and the nationalities diversified greatly? Migration Policy Institute President Andrew Selee and two colleagues who were at the border examining U.S. Customs and Border Protection operations discuss.