The Center for Media and Democracy, in a section entitled "Illegal Immigration US," from its Source Watch website (accessed Jan. 17, 2007), contained the following definition:
"Illegal immigration (also referred to unauthorized or undocumented immigrants) refers to the migration of people across national borders in a way that violates the immigration laws of the destined country."
Barry Chiswick, PhD, Distinguished Professor and Head of the Department of Economics at the University of Illinois at Chicago (UIC), in an essay entitled "Illegal Immigration and Immigration Control," published in the Summer 1988 Journal of Economic Perspectives, explained that:
"By definition, illegal immigration arises from a divergence between whom the United States will accept as an immigrant and the desire of some foreign nationals to live and work in this country. Illegal immigration is as old as U.S. immigration law... With changes in U.S. immigration law and economic and political conditions in the United States and other countries, the nature and characteristics of illegal immigration have also changed."
Demetrios G. Papademetriou, PhD, Director of the Migration Policy Institute (MPI), in a Sep. 1, 2005 Migration Policy Institute essay entitled "The Global Struggle with Illegal Migration: No End in Sight," offered the following explanation:
"Illegal immigration takes several forms, four of which are the most common:
1. Undocumented/unauthorized entrants: These are nationals of one state who enter another state clandestinely. Most such entrants cross land borders, but sea routes are also employed regularly, and wherever inspection regimes are permeable, so are air routes. In all instances, the entrant manages to avoid detection and hence, inspection...
2. Individuals who are inspected upon entry into another state, but gain admission by using fraudulent documents: The fraud in question may involve the person's identity and/or the documentation in support of admission. A variant of this class of entries involves the making of fraudulent asylum claims where issues of identity, documentation, and the narrative in support of the asylum claim may be falsified.
3. Violators of the duration of a visa: These include individuals who enter another state properly but 'willfully' overstay their period of legal stay, thus lapsing into irregular status.
4. Violators of the terms and conditions of a visa: Nationals of one state who enter another state with the proper documents and procedures, but at some point violate the terms of their visa. The most frequent such violation is the acceptance of employment. In a nearly institutionalized variant of such violation, language schools in some countries, such as Japan, have been notorious for admitting students who actually spend their time working. Another variant of this class of violation is when persons with special visa privileges — such as holders of 'border crosser visas' that allow border residents from an adjacent country to reside and be employed in the other country within strictly prescribed time and geographic parameters — systematically abuse these parameters...
Such violations of immigration laws happen with considerable frequency, and, although some are important, most are relatively 'innocent' because they are not systematic and are of short duration. Furthermore, in administrative and regulatory terms, many of these violations are typically the result of inflexible rules and understaffed immigration bureaucracies. More than six million immigration petitions — many of them requests for a change in immigration status — were pending in the US in 2004. Many of these petitioners probably lapsed into illegality during the lengthy adjudication delays."