The principal source of immigration data is the Statistical Yearbook of the Immigration and Naturalization Service, published annually by the Immigration and Naturalization Service (INS), a unit of the Department of Justice. Immigration statistics are prepared from entry visas and change of immigration status forms. Immigrants are aliens admitted for legal permanent residence in the United States. The procedures for admission depend on whether the alien is residing inside or outside the United States at the time of application for permanent residence. Eligible aliens residing outside the United States are issued immigrant visas by the U.S. Department of State. Eligible aliens residing in the United States are allowed to change their status from temporary to permanent residence at INS district offices. The category, immigrant, includes persons who may have entered the United States as nonimmigrants or refugees, but who subsequently changed their status to that of a permanent resident. Nonresident aliens admitted to the United States for a temporary period are nonimmigrants (tables 7 and 432). Refugees are considered nonimmigrants when initially admitted into the United States, but are not included in nonimmigrant admission data. A refugee is any person who is outside his or her country of nationality who is unable or unwilling to return to that country because of persecution or a well-founded fear of persecution.

U.S. immigration law gives preferential immigration status to aliens who are related to certain U.S. citizens or legal permanent residents, aliens with needed job skills, or aliens who qualify as refugees. Immigration to the United States can be divided into two general categories: (1) those subject to the annual worldwide limitation, and (2) those exempt from it. The Immigration Act of 1990 established major revisions in the numerical limits and preference system regulating legal immigration. The numerical limits are imposed on visas issued and not on admissions. The maximum number of visas allowed to be issued under the preference categories in 1993 was 393,690--232,483 for family-sponsored immigrants and 161,207 for employment-based immigrants. There are nine categories among which the family-sponsored and employment- based immigrant visas are distributed, beginning in fiscal year 1991. The family-sponsored preferences are based on the alien's relationship with a U.S. citizen or legal permanent resident (see table 6). The employment-based preferences are: 1) priority workers (persons of extraordinary ability, outstanding professors and researchers, and certain multinational executives and managers); 2) professionals with advanced degrees or aliens with exceptional ability; 3) skilled workers, professionals without advanced degrees, and needed unskilled workers; 4) special immigrants; and 5) employment creation immigrants (investors). Within the overall limitations the per-country limit for independent countries is set to 7 percent of the total family-sponsored and employment-based limits, while dependent areas are limited to two percent of the total. The 1993 limit allowed no more than 27,558 preference visas for any independent country and 7,320 for any dependency. Those exempt from the worldwide limitation include immediate relatives of U.S. citizens, refugees and asylees adjusting to permanent residence, and other various classes of special immigrants.

The Refugee Act of 1980, effective April 1, 1980, provides for a uniform admission procedure for refugees of all countries, based on the United Nations' definition of refugees. Authorized admission ceilings are set annually by the President in consultation with Congress. After one year of residence in the United States, refugees are eligible for immigrant status.

The Immigration Reform and Control Act of 1986 (IRCA) allows two groups of illegal aliens to become temporary and then permanent residents of the United States: aliens who have been in the United States unlawfully since January 1, 1982 (legalization applicants), and aliens who were employed in seasonal agricultural work for a minimum period of time (Special Agricultural Worker (SAW) applicants). The application period for temporary residency for legalization applicants began on May 5, 1987, and ended on May 4, 1988, while the application period for SAW applicants began on June 1, 1987, and ended on November 30, 1988. Legalization applicants became eligible for permanent residence beginning in fiscal year 1989. Beginning 1989 immigrant data include temporary residents who were granted permanent residence under the legalization program of IRCA.