In Constitutional Law, or more specifically Immigration Law, an alien is anyone who is not a national or citizen of the United States. Any number of individuals living or staying within the borders of the United States can be considered aliens. All aliens are non-citizens, but a national is neither a citizen, nor an alien.
The basis for categorizing individuals as aliens is set by the Immigration and Nationality Act of 1952 (INA). The INA defines the different categories to which an individual alien is assigned as follows; resident and non-resident aliens, immigrant and non-immigrant aliens, and documented or undocumented/illegal aliens.
In more general terms, United States federal immigration laws define whether or not an individual is an alien. Federal immigration law also elaborates the legal rights, duties, and obligations of an alien living within the United States, as well as how and whether an alien may pursue naturalization. Naturalization refers to gaining naturalized citizenship, which grants full citizenship rights to any individual who was not born in the United States.
In a sense, the currency for aliens within the United States immigration system is the visa. Different types of visas are granted to aliens based on the purpose and intended duration of their time within the United States. For example, a non-immigrant visa is granted to an alien who intends to stay in the country temporarily for the purpose of business or tourism. Some non-immigrant visas allow the holder to work, others do not.
An immigrant visa, on the other hand, is granted with the idea that the alien will remain in the country permanently, and eventually apply for U.S. citizenship, or nationalized citizenship. Holders of immigrant visas are allowed to work within the country.
According to United States constitutional law, the power to regulate immigration is reserved for United States Congress. In other words, immigration is to be a matter of administrative law, not criminal law. Constitutional law includes all aliens, even undocumented aliens, in the Bill of Rights. In effect, the rights reserved for true citizens of the United States are limited to such activities as voting, holding public office, and holding federal jobs.
This power has been complicated as of the 21st century, in the context of terrorism. In the 21st century, the rights given to aliens have come under particular scrutiny. Discussions have distinguished criminal aliens from law-abiding aliens, often through use of terms such as “alien terrorist.” In 1996, the United States Congress extended its constitutionally delegated regulatory power to the court system by establishing the Alien Terrorist Removal Court. Although, according to constitutional law, constitutional rights are extended to all aliens through the Bill of Rights, an alien who is expected of terrorism may be denied these rights.
