[Excerpt] 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. Since the 1990s, migration control at the border has been guided by a strategy of “prevention through deterrence”—the idea that the concentration of personnel, infrastructure, and surveillance technology along heavily trafficked regions of the border will discourage unauthorized aliens from attempting to enter the United States. Since 2005, CBP has attempted to discourage repeat entries and disrupt migrant smuggling networks by imposing tougher penalties against certain unauthorized aliens, a set of policies known as “enforcement with consequences.” Twenty-five years after the Immigration Reform and Control Act of 1986 (IRCA, P.L. 99-603) marked the beginning of the modern era in border enforcement, this report reviews recent enforcement efforts, takes stock of the current state of border security, and considers lessons that may be learned about a quarter century of enhanced migration control efforts at U.S. borders. IRCA authorized a 50% increase in the size of the USBP, and at least 10 additional laws since then have included provisions related to migration enforcement and/or border security. Appropriations for the USBP have increased about 750% since 1989—a number which excludes many other programs related to border enforcement.