Despite the breadth and complexity of the political system, it is not the only social structure in Nuer culture, and its complexity and order is matched by that of the lineage system. The lineage system overlaps with the political system in several important respects (many tribal segments, for instance, are centered on a dominant clan), but they represent different social structures. The lineage system, ordered around clans, is a genealogical structure built around family relations, whereas the tribal groups are political structures ordered around territories and blood-feuds. The largest genealogical unit in Nuer society is the clan, which is composed of several lineages. Each lineage is agnatic—meaning it is traced along the lines of male descent—and branches out into smaller and smaller lineages, down to individual family units. These lineages are of various sizes, descending from the level of clans to maximal lineages, major lineages, minor lineages, minimal lineages, and families. These lineages are not only abstract genealogical categories, but recognized groups with social functions: “Clans and lineages have names, possess various ritual symbols, and observe certain reciprocal ceremonial relations” (193).

The names and identities of these lineages, however, are relative over time, as new lineages emerge and older clan affiliations pass beyond living memory or become too populous to serve as an efficient marker of group identity.