The genealogy of the Andong Gwon-ssi in the Seongwha period—the oldest extant genealogy in Korean history—offers a unique opportunity to explore political changes and gain insight into the formation of inner circles in Korea during the thirteenth to fifteenth century. Social-network analysis of the marriage networks within this genealogy reveals that for elite families in medieval Korea, marital strategy was as important as ancestry to the maintenance of social/political status.