8 U.S.C. § 1427 : US Code - Section 1427: Requirements of naturalization

    (a) Residence
      No person, except as otherwise provided in this subchapter, shall
    be naturalized unless such applicant, (1) immediately preceding the
    date of filing his application for naturalization has resided
    continuously, after being lawfully admitted for permanent
    residence, within the United States for at least five years and
    during the five years immediately preceding the date of filing his
    application has been physically present therein for periods
    totaling at least half of that time, and who has resided within the
    State or within the district of the Service in the United States in
    which the applicant filed the application for at least three
    months, (2) has resided continuously within the United States from
    the date of the application up to the time of admission to
    citizenship, and (3) during all the periods referred to in this
    subsection has been and still is a person of good moral character,
    attached to the principles of the Constitution of the United
    States, and well disposed to the good order and happiness of the
    United States.
    (b) Absences
      Absence from the United States of more than six months but less
    than one year during the period for which continuous residence is
    required for admission to citizenship, immediately preceding the
    date of filing the application for naturalization, or during the
    period between the date of filing the application and the date of
    any hearing under section 1447(a) of this title, shall break the
    continuity of such residence, unless the applicant shall establish
    to the satisfaction of the Attorney General that he did not in fact
    abandon his residence in the United States during such period.
      Absence from the United States for a continuous period of one
    year or more during the period for which continuous residence is
    required for admission to citizenship (whether preceding or
    subsequent to the filing of the application for naturalization)
    shall break the continuity of such residence, except that in the
    case of a person who has been physically present and residing in
    the United States, after being lawfully admitted for permanent
    residence, for an uninterrupted period of at least one year, and
    who thereafter is employed by or under contract with the Government
    of the United States or an American institution of research
    recognized as such by the Attorney General, or is employed by an
    American firm or corporation engaged in whole or in part in the
    development of foreign trade and commerce of the United States, or
    a subsidiary thereof more than 50 per centum of whose stock is
    owned by an American firm or corporation, or is employed by a
    public international organization of which the United States is a
    member by treaty or statute and by which the alien was not employed
    until after being lawfully admitted for permanent residence, no
    period of absence from the United States shall break the continuity
    of residence if - 
        (1) prior to the beginning of such period of employment
      (whether such period begins before or after his departure from
      the United States), but prior to the expiration of one year of
      continuous absence from the United States, the person has
      established to the satisfaction of the Attorney General that his
      absence from the United States for such period is to be on behalf
      of such Government, or for the purpose of carrying on scientific
      research on behalf of such institution, or to be engaged in the
      development of such foreign trade and commerce or whose residence
      abroad is necessary to the protection of the property rights in
      such countries in such firm or corporation, or to be employed by
      a public international organization of which the United States is
      a member by treaty or statute and by which the alien was not
      employed until after being lawfully admitted for permanent
      residence; and
        (2) such person proves to the satisfaction of the Attorney
      General that his absence from the United States for such period
      has been for such purpose.

    The spouse and dependent unmarried sons and daughters who are
    members of the household of a person who qualifies for the benefits
    of this subsection shall also be entitled to such benefits during
    the period for which they were residing abroad as dependent members
    of the household of the person.
    (c) Physical presence
      The granting of the benefits of subsection (b) of this section
    shall not relieve the applicant from the requirement of physical
    presence within the United States for the period specified in
    subsection (a) of this section, except in the case of those persons
    who are employed by, or under contract with, the Government of the
    United States. In the case of a person employed by or under
    contract with Central Intelligence Agency, the requirement in
    subsection (b) of this section of an uninterrupted period of at
    least one year of physical presence in the United States may be
    complied with by such person at any time prior to filing an
    application for naturalization.
    (d) Moral character
      No finding by the Attorney General that the applicant is not
    deportable shall be accepted as conclusive evidence of good moral
    character.
    (e) Determination
      In determining whether the applicant has sustained the burden of
    establishing good moral character and the other qualifications for
    citizenship specified in subsection (a) of this section, the
    Attorney General shall not be limited to the applicant's conduct
    during the five years preceding the filing of the application, but
    may take into consideration as a basis for such determination the
    applicant's conduct and acts at any time prior to that period.
    (f) Persons making extraordinary contributions to national security
      (1) Whenever the Director of Central Intelligence, the Attorney
    General and the Commissioner of Immigration determine that an
    applicant otherwise eligible for naturalization has made an
    extraordinary contribution to the national security of the United
    States or to the conduct of United States intelligence activities,
    the applicant may be naturalized without regard to the residence
    and physical presence requirements of this section, or to the
    prohibitions of section 1424 of this title, and no residence within
    a particular State or district of the Service in the United States
    shall be required: Provided, That the applicant has continuously
    resided in the United States for at least one year prior to
    naturalization: Provided further, That the provisions of this
    subsection shall not apply to any alien described in clauses (i)
    through (v) of section 1158(b)(2)(A) of this title.
      (2) An applicant for naturalization under this subsection may be
    administered the oath of allegiance under section 1448(a) of this
    title by any district court of the United States, without regard to
    the residence of the applicant. Proceedings under this subsection
    shall be conducted in a manner consistent with the protection of
    intelligence sources, methods and activities.
      (3) The number of aliens naturalized pursuant to this subsection
    in any fiscal year shall not exceed five. The Director of Central
    Intelligence shall inform the Select Committee on Intelligence and
    the Committee on the Judiciary of the Senate and the Permanent
    Select Committee on Intelligence and the Committee on the Judiciary
    of the House of Representatives within a reasonable time prior to
    the filing of each application under the provisions of this
    subsection.