Border enforcement is a type of immigration enforcement whereby a country enforces its immigration laws by trying to prevent people from crossing its border or borders illegally. There are multiple methods a country can use to do this, including patrolling its border and building walls along part or all of it.[1] The term is most commonly used in regards to the efforts by the United States government to prevent people from migrating illegally to the U.S. by crossing the Mexico–United States border. Since 2002, the number of United States Border Patrol agents has more than doubled, to a total of 20,273 (as of September 2016), and federal spending on the Patrol has increased from $1.4 to $3.8 billion over the same time.[2] In addition to the Patrol, agencies responsible for border enforcement in the U.S. include Immigration and Customs Enforcement.[3]