Unauthorized immigration to the United States.

"This paper surveys research on the size of the undocumented immigrant population in the United States, the causes and consequences of illegal migrant flows, public attitudes toward unauthorized migrants, and the history of attempts to control the volume of undocumented migration. It concludes that there are powerful push and pull factors that create and sustain the volume of unauthorized migration, that there is little evidence that undocumented migrants have negative labor market consequences despite what the general public thinks, that U.S. policy has been largely powerless to make a permanent dent in undocumented immigration, and that the current level of clandestine U.S. immigration may not be far from what society might view as socially optimal." excerpt