"Family reunification is a key principle underlying U.S. immigration policy. It is embodied in the Immigration and Nationality Act (INA), which specifies numerical limits for five family-based admission categories, as well as a per-country limit on total family-based admissions. The five categories include immediate relatives of U.S. citizens and four other family-based categories that vary according to individual characteristics such as the legal status of the petitioning U.S.-based relative, and the age, family relationship, and marital status of the prospective immigrant. Of the 1.03 million foreign nationals admitted to the United States in FY2012 as lawful permanent residents (LPRs), 680,799, or 66%, were admitted on the basis of family ties. Of these family-based immigrants admitted in FY2012, 70% were admitted as immediate relatives of U.S. citizens. Many of the 1.03 million immigrants were initially admitted on a legal temporary basis and became immigrants by converting or 'adjusting' their status to a lawful permanent resident. The proportion of family-based immigrants who adjusted their immigration status while residing in the United States (53%) exceeded that of family-based immigrants who had their immigration petitions processed while living abroad (47%), although such percentages varied considerably among the five family-based admission categories. Since FY2000, increasing numbers of immediate relatives of U.S. citizens have accounted for all of the growth in family-based admissions. Between FY2000 and FY2009, immigrants who accompanied or later followed principal (qualifying) immigrants averaged 12% of all family-based admissions annually. During that period, Mexico, the Philippines, China, India, and the Dominican Republic sent the most family-based immigrants to the United States."
CRS Report for Congress, R43145