Border enforcement is a core element of the Department of Homeland Security's (DHS's) effort to control illegal migration, with the U.S. Border Patrol (USBP) within the Bureau of 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 decade following the terrorist attacks of 2001. This book reviews border enforcement efforts in the 25 years since the Immigration Reform and Control Act of 1986 (IRCA) initiated the modern era in migration control with a focus on appropriations and resources dedicated to border enforcement, indicators of enforcement outcomes, and possible secondary and unintended consequences of border enforcement.