Nonimmigrants, whose annual admissions to the United States sometimes exceed ten million, constitute a major classification in the study of immigration law. Most of them, coming as tourists or in connection with business, are important to the economy of the United States; others as students, artists, researchers or teachers, participate in the academic, cultural and scientific activities that are essential to the country's vitality. Nonimmigrants are numerically limited in the H-1B and H-2B categories; they can usually overcome, more easily than the immigrant, any qualitative ground of exclusion; and are likely to be able to obtain their visas in hours or days rather than the years usually faced by immigrants.

Unlike the lawful immigrant, however, who is admitted to the United States for permanent residence (green card), the nonimmigrant may remain only for the duration of an authorized stay and engage only in those activities that are compatible with the specific nonimmigrant status given on admission. The nonimmigrant whose employment or other activities exceed the bounds of that status, or who fails to depart on time, is deportable for having “failed to maintain the nonimmigrant status in which the alien was admitted. ...”

While no single classification may offer all of the advantages of lawful permanent residence, nonimmigrant status is sometimes otherwise preferable. Apart from the relative speed and informality of securing a nonimmigrant status, it may adequately suit an alien's needs, it obviates selective service liability (military service), and it may cost less in taxes. Which nonimmigrant class to choose, when the alien qualifies for more than one, may involve tax considerations, ease of proof, time constraints, and other factors.