This report presents the results to date of a three-year archaeological investigation of the Postclassic and early Spanish Colonial Mixtec City of Yucundaa, PuebloViejo de Teposcolula, Oaxaca. It is the first project in Oaxaca to focus specifically on a major prehispanic city and its dramatic transformation during the first three decades of the colonial period. Given the dearth of conventional historical documentation relating to Yucundaa, the site itself serves as a “primary text,” the major source of information regarding its development and operation. The project attempts to define the major components of the settlement, and to examine each as comprehensively as possible in order to form a coherent view of the city's structure and function. At the conclusion of the third season, the encouraging results serve to demonstrate the utility of a well-planned excavation program that from its inception attempts to examine an entire Postclassic-Colonial settlement and the great transformation occurring there between A.D. 1521 and 1550. The research methods, as well as information and insights derived from the project, will provide stimulus and a useful model for the study of other Mesoamerican urban settlements.