Border enforcement is a core element of the Department of Homeland Security's effort to control unauthorised migration, with the U.S. Border Patrol (USBP) within the U.S. Customs and Border Protection (CBP) as the lead agency along most of the border. Border enforcement has been an ongoing subject of congressional interest since the 1970s, when illegal immigration to the United States first registered as a serious national problem; and border security has received additional attention in the years since the terrorist attacks of 2001. This book reviews efforts to combat unauthorised migration across the Southwest border in the nearly three decades since IRCA initiated the modern era in migration control. In reviewing such efforts, the book takes stock of the current state of border security and considers lessons that may be learned about enhanced enforcement at U.S. borders. Furthermore, the title discusses key statutory authorities and requirements governing DHS's construction of barriers along the U.S. borders. It also includes appendixes listing federal laws that have been waived by DHS in furtherance of border construction projects.