How does the Immigration and Nationality Act define the term 'alien'?

1. The statutory definition — simple, broad, and authoritative

The INA’s operative definition appears in section 101(a)^[1]: “alien” means any person not a citizen or national of the United States,” language reproduced in official U.S. Code and government compilations ^{[2] [3]}. This is the baseline legal meaning courts, agencies, and Congress refer to when a statute or regulation speaks of “aliens” ^[3].

2. How agencies apply the definition in practice

Federal agencies use the INA definition when building rules and programs that mention “aliens.” For example, USCIS materials explain that Title 8 of the U.S. Code covers “Aliens and Nationality,” and the INA contains many of the immigration law provisions that govern persons who meet the statutory “alien” definition ^[5]. DHS and ICE rules and program pages also treat “alien” consistent with the INA when describing whom registration, enforcement, or detention authorities cover ^{[6] [7]}.

3. Policy language vs. statutory language — “noncitizen” and other substitutes

While the statute’s definition is fixed, policy documents have moved toward alternative vocabulary. USCIS updated its Policy Manual to replace some instances of the word “alien” with “noncitizen” or other terms where appropriate, explicitly noting that those substitutions reference the INA definition in section 101(a)^[1] — i.e., the underlying legal meaning does not change even when terminology does ^[4]. This reflects sensitivity to public perception and clarity, but not a legal redefinition ^[4].

4. Where the definition matters — examples of downstream effects

The INA definition is the hinge for many substantive rules: who must register, who may be detained or removed, who is presumptively an immigrant for visa interviews, and who falls within criminal or administrative provisions. For instance, regulatory and enforcement materials discuss “aliens” in contexts ranging from registration and fingerprinting obligations to categories of inadmissibility and removal ^{[7] [8] [6]}. Congressional bills and reports routinely cite “the meaning given such term in section 101 of the INA” when they define their own sense of “alien” for reporting or enforcement purposes ^[9].

5. Nuances, exceptions, and related terms the statute does not alter

The single-line definition does not itself enumerate subcategories (e.g., lawful permanent residents, nonimmigrants, refugees, diplomats) — those classifications are created elsewhere in the INA and regulations. Some statutory provisions explicitly carve out exceptions or define particular classes (for example, nonimmigrant subclasses in 101(a)^[10] or diplomatic exemptions), so being an “alien” does not by itself determine rights or remedies; those depend on further status-based rules ^{[2] [8]}. Available sources do not mention any alternate statutory definition of “alien” beyond 101(a)^{[1] [2] [3]}.

6. Political and communicative implications — why terminology matters

Although the legal meaning is straightforward, the word “alien” carries political and social weight. That has prompted agencies to adopt “noncitizen” in some contexts for clarity and to reduce perceived stigma, while enforcement-focused offices and statutes continue to use the legal term where precision matters ^{[4] [6]}. Legislative proposals and executive actions that reference “aliens” typically invoke the INA definition when specifying who is subject to a policy or penalty ^{[9] [11]}.

7. Bottom line for readers and practitioners

Legally, refer to 8 U.S.C. § 1101(a)^[1]: an “alien” is anyone who is not a U.S. citizen or national; that statutory text drives how agencies and courts treat the term even when alternative labels are used in policy texts ^{[2] [3] [4]}. For specific rights, duties, or exceptions you must look to the particular INA sections and regulations that classify different kinds of aliens ^{[2] [8]}.