In the United States, federal immigration law determines whether a person is an alien, as well as associated legal rights, duties, and obligations of aliens in the United states. It also provides means by which certain aliens can become naturalized citizens with full rights of citizenship. Immigration law serves as a gatekeeper for the nation's border: it determines who may enter, how long they may stay and when they must leave.

The United States has a long history of immigration laws. The Immigration and Nationality Act of 1952, (INA) with some major, and many minor changes, continues to be the basic immigration law of the country. The most significant amendment to the INA was in 1965 which abolished the natural origin provisions, and established a new quota system.

For INA purposes, an "alien" is any person who is not a citizen or a national of the United States. There are different categories of aliens: resident and nonresident, immigrant and nonimmigrant, documented and undocumented.

Congress has total and complete authority over immigration. Power of the President is limited to policies on refugees. Unless the issue concerns the rights of aliens to constitutional protections the courts have rarely intruded. States have limited legislative authority regarding immigration, and 28 U.S.C. § 1251 details the full extent of state jurisdiction.

The need to stem illegal immigration prompted Congress to enact the Immigration Reform and Control Act (IRCA) of 1986. The IRCA toughened criminal sanctions for employers who hire illegal aliens, denied illegal aliens federally funded welfare benefits, and legitimized some aliens through an amnesty program. The Immigration Marriage Fraud Amendments of 1986 sought to limit the practice of marrying to obtain citizenship. The Immigration Act of 1990 thoroughly revamped the INA making allocation of visas more even among foreign nations, eliminating archaic rules, and increasing the level of worldwide immigration.

The goals in immigration policies are achieved by granting or denying visas. There are two types of visas: immigrant and nonimmigrant.

Nonimmigrant visas are primary issued to tourists and temporary business visitors. Nonimmigrant visas are divided into eighteen main categories, and the number of visas in most categories are not limited. Only a few categories of non-immigrant visas allow their holders work in the United States.

Immigrant visas permit their holders to stay in the United States permanently and ultimately to apply for citizenship. An alien who has an immigrant visa is permitted to work in the United States. Congress limits the overall number of immigrant visas, which was 675,000 in 1995. Many immigrant visas are also subject to per-country caps.