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
No appendices available at this time.
Technical Update - Replacing the Term “Foreign National”October 08, 2019
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”].
POLICY ALERT - Comprehensive Citizenship and Naturalization Policy GuidanceJanuary 07, 2013
USCIS is issuing updated and comprehensive citizenship and naturalization policy guidance in the new USCIS Policy Manual.