Prior efforts to identify traditional socio-territorial groups among the Central Yup'ik Eskimos of southwestern Alaska have been primarily theoretical in nature, examined the subject from very restricted temporal perspectives, and were heavily reliant on a small body of written historical accounts---none of which were informed by contacts with indigenous populations across the entire region. The collective results are inconsistent and largely unverifiable; hence many basic details about Yup'ik socio-territorial organization remain obscure. This study deviates from its predecessors in geographical focus, temporal scope and methodology. The geographical focus is on the Nuniwarmiut (or Nunivak Eskimos), both the most isolated and best documented of all Central Yup'ik populations. Its temporal scope covers a period of 80 years, the earliest point of which marks the practical limits of reliability of the available ethnographic data. Finally, the study's methodology is ethnohistorical; it employs a rich array of complementary historical, ethnographic and archeological data to produce a far more detailed account of socio-territorial organization than has been compiled for any other population in the region. The findings indicate socio-territorial organization among the Nuniwarmiut took the form of local groups organized around winter villages. The functional stability of each group was susceptible to various natural and cultural factors; in fact, such groups ranged in number from as many as 30 to as few as 7 over the course of the study period. The Nuniwarmiut society was a level of identity above the local group; it was comprised of the totality of local groups that existed at any point in time, but was not itself a socio-territorial unit. Overall, the study demonstrates that socio-territorial organization among the Nuniwarmiut was substantially more complex and dynamic than previously recognized.