Khubilai khan's ceremonious adoption of Chinese dynastic forms in 1272 began the period of greatest Mongolian adaptation to Chinese influences on the patterns of government. This chapter attempts to suggest the kinds of issues in social history that give the Yüan dynasty its interest and importance in the minds of historians today. The uncertainty about the size and distribution of the Chinese population in Yüan society remains subject to speculation and debate. The chapter shows that the Yüan government went beyond all precedent in its effort to classify and register its subjects according to status and occupation, in order to serve its social management objectives. The fourfold ethnically defined system of social classes: Mongols, Western Asians, Han jen, and Nan jen, did not eliminate the preexisting Chinese elite or attempt to reduce all Chinese to one debased economic level, neither did it ensure superior economic status for all Mongols and Western Asians.