Nigeria

(1) The following persons are citizens of Nigeria by birth namely –
(a) every person born in Nigeria before the date of independence, either of whose parents or any of whose grandparents belongs or belonged to a community indigenous to Nigeria:
Provided that a person shall not become a citizen of Nigeria by virtue of this section if neither of his parents nor any of his grandparents was born in Nigeria;
(b) every person born in Nigeria after the date of independence either of whose parents or any of whose grandparents is a citizen of Nigeria; and
(c) every person born outside Nigeria either of whose parents is a citizen of Nigeria.
(2) In this section, “the date of independence” means the 1st day of October 1960. (Sec. 25)

(1) Subject to the provisions of section 28 of this Constitution, a person to whom the provisions of this section apply may be registered as a citizen of Nigeria, if the President is satisfied that –
(a) he is a person of good character;
(b) he has shown a clear intention of his desire to be domiciled in Nigeria; and
(c) he has taken the Oath of Allegiance prescribed in the Seventh Schedule to this Constitution.
(2) the provisions of this section shall apply to –
(a) any woman who is or has been married to a citizen of Nigeria; or
(b) every person of full age and capacity born outside Nigeria any of whose grandparents is a citizen of Nigeria. (Sec. 26)

(1) Any citizen of Nigeria of full age who wishes to renounce his Nigerian citizenship shall make a declaration in the prescribed manner for the renunciation.
(2) The President shall cause the declaration made under subsection (1) of this section to be registered and upon such registration, the person who made the declaration shall cease to be a citizen of Nigeria.
(3) The President may withhold the registration of any declaration made under subsection (1) of this section if –
(a) the declaration is made during any war in which Nigeria is physically involved; or
(b) in his opinion, it is otherwise contrary to public policy.
(4) For the purposes of subsection (1) of this section –
(a) “full age” means the age of eighteen years and above;
(b) any woman who is married shall be deemed to be of full age. (Sec. 29)

(1) The president may make regulations, not inconsistent with this Chapter,² prescribing all matters which are required or permitted to be prescribed or which are necessary or convenient to be prescribed for carrying out or giving effect to the provisions of this Chapter, and for granting special immigrant status with full residential rights to non-Nigerian spouses of citizens of Nigeria who do not wish to acquire Nigerian citizenship.
… (Sec. 32)

Notwithstanding the provisions of Chapter III³ of this Constitution but subject to section 28 thereof, any person who became a citizen of Nigeria by birth, registration or naturalisation under the provisions of any other Constitution shall continue to be a citizen of Nigeria under this Constitution. (Sec. 309)

…
9. Citizenship, naturalisation and aliens.
… (Second Schedule – Legislative Powers, Part I – Exclusive Legislative List)