Kin Groups and Descent. Lak society is characterized by dual organization: every Lak belongs to either "Bongian" (sea eagle, Haliaetus leucogaster ) or "Koroe" (fish hawk, Pandion leucocephalus ) moiety; and members of one moiety must marry into the other. Each village is considered Bongian or Koroe, depending on the dominant landowning segment in the area. This designation is important for rituals that regulate relations between moieties. Thus, the first time a member of the opposite moiety sleeps or dances in the village, he will be showered with gifts, which must, however, be repaid shortly after. Recruitment to moiety and clan membership is matrilineal. Lak clans are thus partitioned into two sets. Interestingly, two of the largest Lak clans bear the same names as the moieties, suggesting that the other clans are perhaps newer to the region. Lineages are demarcated by their right to erect men's houses; they also have ancestors who are invoked in men's ritual.
Kinship Terminology. Kinship terminology is of the Iroquois type. Affinal terms are extended to all members of the opposite moiety.