On the basis of extensive evidence indicating that large numbers of Indian children were being separated from their families and tribes and were being placed in non-Indian homes through state adoption, foster care, and parental rights termination proceedings, and that this practice caused serious problems for the children, their parents, and their tribes, Congress enacted the Indian Child Welfare Act of 1978 (ICWA), which, inter alia, gives tribal courts exclusive jurisdiction over custody proceedings involving an Indian child "who resides or is domiciled within" a tribes reservation. This case involves the status of twin illegitimate babies, whose parents were enrolled members of appellant Tribe and residents and domiciliaries of its reservation in Neshoba County, Mississippi. After the twins births in Harrison County, some 200 miles from the reservation, and their parents execution of consent-to-adoption forms, they were adopted in that countys Chancery Court by the appellees Holyfield, who were non-Indian. That court subseq