This article statistically analyzes quantitative data from numerous sources in order to assess changes in marriage patterns, family structure, and rates of social mobility during the period from 1282 to 1494. During this period, three systems of social stratification coexisted -- wealth, political office, and age of family -- but these contending status systems were not consistent in their rankings of families. Each status system was conservative in the sense that elite families at the top of that hierarchy married each other in order to stabilize their position. But because of inconsistency in rankings, contradiction within the elite opened up the Florentine marriage system to widespread upward social mobility by new men. In their own families, successful new men aggressively imitated their economically and politically declining status superiors. Sharp class divisions thereby blurred into continuous and negotiable status gradients. These open-elite patterns of social mobility, present throughout the early Florentine Renaissance, were most extreme during the Albizzi regime, immediately following the Ciompi Revolt.