Defining ethnicity in archeological settlements is a major methodological problem in the South Central Andes. In this region, pre-Hispanic political and economic organization has been understood within the theoretical framework known as zonal complementarity or verticality. Due to a process of direct colonization by independent polities in key ecological zones, these models are characterized by a striking regional ethnic heterogeneity in space and time. The use of the household as an analytical unit is proposed as the most successful means of defining ethnically distinct populations in pre-Hispanic contexts. This methodology is applied to Late Intermediate period (ca. A.D. 1000–1475) sites in the Osmore Drainage of southern Peru. Two domestic architectural types are defined that are hypothesized to correspond to ethnically distinct groups. Excavation data are analyzed to further differentiate these household types and provide a framework for addressing the dynamics of pre-Hispanic cultural process in the South Central Andes.