Federal immigration law determines whether a person is an alien, and 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 determines who may enter, how long they may stay and when they must leave.
The main legislation governing immigration is the Immigration and Nationality Act of 1952, (INA). The act hads been amended numerous times, the most significant of which was the establishment of a new quota system in 1965. 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 ("illegal" ).
Today, the main immigration statute, the Immigration and Nationality Act (INA), is codified as Title 8 of the United States Code (U.S.C.). While the INA provides the basic structure of the immigration system, the various governmental agencies that administer the immigration laws promulgate regulations to implement the statute. These regulations are published in the Federal Register, and incorporated into the Code of Federal Regulations (C.F.R.). Such regulations must be consistent, however, with the statute, as well as the U.S. Constitution.
Immigration policies are implemented 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. 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, and many immigrant visas are also subject to per-country caps.
There are detailed regulations covering grounds for inadmissibility and exceptions. For example, section 212 of the Immigration and Naturalization Act sets forth rules governing inadmissibility of those convicted of crimes and exceptions, based upon factors such as the type of crime, date of conviction, and sentence received.