(a) Tribal government Indian child and family service programs. Any person meeting the definition of Indian, Indian child, Indian custodian, or Indian parent of any unmarried person under the age of 18 as defined in § 23.2 is eligible for services provided under 25 U.S.C. 1931 of the Act. Tribal membership status shall be determined by tribal law, ordinance, or custom. The tribe may, under subpart C, extend services to nontribal family members related by marriage to tribal members, provided such services promote the intent and purposes of the Act. A tribe may also, within available resources, extend services under this part to individuals who are members of, or are eligible for membership in other Indian tribes, and who reside within the tribe's designated service area.

(b) Off-reservation Indian child and family service programs and agreements with the Secretary of Health and Human Services pursuant to 25 U.S.C. 1933. For purposes of eligibility for services provided under 25 U.S.C. 1932 and 1933 of the Act, any person meeting the definition of Indian, Indian child, Indian custodian, or Indian parent of any unmarried person under the age of 18 as defined in § 23.2, or the definition of Indian as defined in 25 U.S.C. 1603(c), shall be eligible for services. Tribal membership status shall be determined by tribal law, ordinance, or custom.