There are many sources of law governing immigration. First among these is the United States Constitution. A main source of immigration law is statutes (laws, public laws) enacted by Congress. Most of the laws affecting immigration are contained in the Immigration and Nationality Act, often referred to as "the Act" or simply as the "INA." Although the provisions (terms) of most statutes affecting immigration are reflected in the INA, many are not codified in the INA and must be found in the original legislation in which they were enacted.

Statutes usually provide broad authority and apply to general situations. Agencies must take the general provisions of the statute and apply them to specific, detailed situations. The INS regulations serve this purpose. There are immigration laws that involve other agencies in addition to the INS. For example, both the Department of Labor and Department of State are involved in the administration of the immigration laws. You can find these additional regulations here (Other Immigration CFRs).

One source of legal interpretations of immigration laws and regulations are administrative decisions. The Board of Immigration Appeals is a separate agency within the Department of Justice that reviews immigration cases and issues appellate administrative decisions that are binding on the INS nationwide.