"The United States Border Patrol (USBP) has a long and storied history as our nation's first line of defense against unauthorized migration. Today, the USBP's primary mission is to detect and prevent the entry of illegal aliens into the country, assist in the detection of possible terrorists, and interdict drug smugglers and other criminals. The Homeland Security Act of 2002 dissolved the Immigration and Naturalization Service and placed the USBP within the Department of Homeland Security (DHS). Within DHS, the USBP forms a part of the Bureau of Customs and Border Protection under the Directorate of Border and Transportation Security. During the last decade, the USBP has seen its budget and manpower more than triple. This expansion was the direct result of Congressional concerns about illegal immigration and the agency's adoption of "Prevention Through Deterrence" as its chief operational strategy in 1994. The strategy calls for placing USBP resources and manpower directly at the areas of greatest illegal immigration in order to detect, deter, and apprehend aliens attempting to cross the border between official points of entry. Post 9/11, the USBP has also refocused its strategy on preventing the entry of terrorists and weapons of mass destruction. In addition to a workforce of over 10,000 agents, the USBP deploys vehicles, aircraft, watercraft, and many different technologies to defend the border."
CRS Report for Congress, RL32562