THE PREVALENCE of preferential father's brothers' daughter marriage in the Middle East, and its association with Islam, has frequently received reference. Yet no clear picture of the possible structural implications of this form of preferential marriage has emerged, nor of the actual distribution and frequency of the practice. The present paper attempts to analyze the relationship between the Kurdish form of segmentary lineage organization and this marriage pattern. Any chart of unilineal descent in a stable or expanding population constitutes a ramifying system where succeeding generations in many lines tend to be larger and more inclusive than the preceeding. It is this chart, generally in compressed form, which is utilized to organize a descent group in the form of a segmentary lineage organization. This organizational form was named by Gifford and later by Firth, who called it a "ramage," and first analyzed fully by Evans-Pritchard.' Recent work on this type of organization has been lucidly summarized by Fortes.2 In almost all the lineage systems described in the literature, the lineage, or the clan of which it is a part, is an exogamous group. This fact of exogamy has important implications, e.g. for the development of dispersed clans and normalizing of a "daughter's son" relationship as a mechanism for grafting foreign lineages to the dominant lineage of an area (as described for the Nuer), and it is further frequently reflected in the whole construction of kinship terminology.3 Lineage exogamy is, however, no essential feature of lineage systems. No matter what the marriage pattern in a population may be, a strict chart of unilineal descent offers an equally clear framework on which a segmentary lineage organization may be based. In a patrilineal system, matrilineal ties may be regarded as totally irrelevant to the political relations of segments and whole lineages-marriage patterns may, so to speak, be "liberated" from their role in defining the relations between political groups. This lack of association of lineage organization and exogamy is common among Semitic and Iranian tribes of the Middle East,