Kin Groups and Descent. The basic socioeconomic unit of the Sirionó is the monogamous nuclear family; only chiefs could have several wives. Extended families are exogamous, and the chief of the band chooses the bride. Postmaritial residence is uxorilocal until the birth of the first children. There is no concept of lineage or unilineal descent.
Kinship Terminology. On the basis of a terminological equivalence between father's sister's daughter and father's sister, the Sirionó kinship system has sometimes been regarded as being of the Crow type. In several other crucial respects, however, the system does not conform to the Crow pattern or to its underlying logic. Traces of parallel transmission of certain statuses have been noted. Terminological equivalence of a wife's siblings with mother's brother's children and of husband's siblings with father's sister's children are consistent with potential asymmetric cross-cousin marriage.