Chapter 1 - Purpose and Background
USCIS conducts an investigation and examination of all naturalization applicants to determine whether an applicant meets all pertinent eligibility requirements to become a U.S. citizen. The investigation and examination process encompasses all factors relating to the applicant's eligibility: 
Completion of security and criminal background checks;
Review of the applicant’s complete immigration record;
In-person interview(s) with oral and written testimony;
Testing for English and civics requirements; and
Qualification for a disability exception.
USCIS officers have authority to conduct the investigation and examination.  The authority includes the legal authority for certain officers to administer the Oath of Allegiance, obtain oral and written testimony during an in-person interview, subpoena witnesses, and request evidence. 
The applicant has the burden of establishing eligibility by a preponderance of the evidence throughout the examination.  The officer must resolve any pending issues and obtain all of the necessary information and evidence to make a decision on the application. Uniformity in decision-making and application processing is vital to the integrity of the naturalization process. Consistency in the decision-making process enhances USCIS’ goal to ensure that the relevant laws and regulations are applied accurately to each case.
Beginning in 1906, a complete examination and questioning under oath was required of the “petitioner” (now “applicant”) for naturalization and his or her witnesses at the final hearing for naturalization in court.  Congress amended the statute in 1940 to include English language requirements and a provision for questioning applicants on their understanding of the principles of the Constitution. 
Today, USCIS conducts an investigation and examination of all applicants for naturalization to determine their eligibility for naturalization, including the applicant’s lawful admission for permanent residence, ability to establish good moral character, attachment to the Constitution, residence and physical presence in the United States, and the English and civics requirements for naturalization.
[^ 5] In 1981, Congress enacted legislation which eliminated the character witness requirements of naturalization, though USCIS has the authority to subpoena witnesses if necessary.
[^ 6] See the Nationality Act of 1940, Pub. L. 76-853, 54 Stat. 1137 (October 14, 1940).
8 CFR 2 - Authority of the Secretary of the Department of Homeland Security
INA 318 - Prerequisite to naturalization, burden of proof
Before October 29, 2019, USCIS considered children of members of the U.S. armed forces or U.S. government employees, who were stationed outside of the United States, to meet the requirement of “is residing in” the United States for the purpose of acquiring citizenship under INA 320. This interpretation was consistent with the definition of “residence” for purposes of naturalization under INA 316. Based on this treatment of U.S. government employees and their children in the context of naturalization under INA 316, USCIS determined that “residing in the United States” for purposes of acquisition of citizenship under INA 320 should likewise be interpreted to include children of U.S. military and government employees stationed outside of the United States who were residing with their parents.
This interpretation, however, was inconsistent with other provisions of the Immigration and Nationality Act (INA), including the definition of “residence” at INA 101(a)(33) and language in INA 322(a) and INA 322(d), which suggested that the citizenship of military children residing outside of the United States should be considered under that provision rather than under INA 320. Effective October 29, 2019, USCIS amended its policy guidance to address these concerns, and determined that children of members of the U.S. armed forces or U.S. government employees stationed outside of the United States would not be eligible for citizenship acquisition under INA 320.
On March 26, 2020, the Citizenship for Children of Military Members and Civil Servants Act was enacted, amending INA 320, so that a child residing with his or her U.S. citizen parent, who is stationed outside of the United States as a member of the U.S. armed forces or a U.S. government employee, or is residing in marital union with a member of the U.S. armed forces or a U.S. government employee who is stationed outside of the United States, acquires citizenship under INA 320 if all requirements of INA 320(c) and INA 320(a)(1)-(2) are met. In line with the statute, USCIS rescinds its previous guidance, clarifying that these children are eligible to acquire citizenship under INA 320 if all other requirements under INA 320 are met.
The amendment to INA 320 applies to children who were under the age of 18 on March 26, 2020.
[^ 1] Even though the child of a member of the U.S. armed forces or U.S. government employee stationed outside of the United States may be eligible to apply for a Certificate of Citizenship under INA 322 since he or she resides outside of the United States, USCIS interpreted the child to meet residency requirements under INA 320 as well, which formerly required the child to be residing in the United States with his or her parent to acquire citizenship.
[^ 2] For example, U.S. government employees, including members of the U.S. armed forces, are eligible to apply for an exception to the continuous residence requirement for naturalization under INA 316 as long as their residency outside of the United States was on behalf of the U.S. government. See INA 316(b). See INA 316(a). See Part D, General Naturalization Requirements, Chapter 3, Continuous Residence [12 USCIS-PM D.3].
[^ 3] See Policy Manual Technical Update, Child Citizenship Act and Children of U.S. Government Employees Residing Abroad (July 20, 2015); and Acquisition of Citizenship by Children of U.S. Military and Government Employees Stationed Abroad under Section 320 of the Immigration and Nationality Act (INA), No. 103, issued May 6, 2004.
[^ 4] See USCIS Policy Alert, Defining “Residence” in Statutory Provisions Related to Citizenship [PA-2019-05] (PDF, 308.45 KB). This Policy Alert has been superseded by Policy Manual updates to reflect changes made under Pub. L. 116-133 (PDF).
U.S. Citizenship and Immigration Services (USCIS) is updating and incorporating relevant Adjudicator’s Field Manual (AFM) content into the USCIS Policy Manual. As that process is ongoing, USCIS has moved any remaining AFM content to its corresponding USCIS Policy Manual Part, in PDF format, until relevant AFM content has been properly incorporated into the USCIS Policy Manual. To the extent that a provision in the USCIS Policy Manual conflicts with remaining AFM content or Policy Memoranda, the updated information in the USCIS Policy Manual prevails. To find remaining AFM content, see the crosswalk (PDF) between the AFM and the Policy Manual.
This technical update replaces all instances of the term “foreign national” with “alien” throughout the Policy Manual as used to refer to a person who meets the definition provided in INA 101(a)(3) [“any person not a citizen or national of the United States”].
USCIS is issuing updated and comprehensive citizenship and naturalization policy guidance in the new USCIS Policy Manual.