The site of a great Ancestral Pueblo center in the 11th and 12th centuries AD, the ruins in Chaco Canyon look like a city to some archaeologists, a ceremonial center to others. Chaco and the people who created its monumental great houses, extensive roads, and network of outlying settlements remain an enigma in American archaeology, although all agree they were exceptional in Southwestern prehistory.Two decades after the latest and largest program of field research at Chaco?the National Park Service's "Chaco Project" (1971?1982)?the original researchers and other leading Chaco scholars convened to evaluate what they now know about Chaco in light of new theories and new data.Those meetings culminated in an advanced seminar at the School of American Research, where the Chaco Project itself was born in 1968. In this capstone volume, the contributors address central archaeological themes, including environment, organization of production, architecture, regional issues, and society and polity.They place Chaco in its time and in its region, considering what came before and after its heyday and its neighbors to the north and south, including Mesoamerica. Society of American Archaeology president Lynne Sebastian sums up the volume and more than thirty years of research with compelling observations and conclusions on the Chaco Project of the 1970s, the "Chaco synthesis" of the 1990s, and the continuing possibilities for archaeology at Chaco Canyon.