Today’s mathematics of complex systems offer a variety of tools to investigate the macroscopic properties of interactions that occur along a temporal dimension. By tracing patterns of interaction among the elements of a system, one can often discover emergent properties at a higher level. In retrospect it seems remarkable that a few simple insights from the formal analysis of complex sys-tems should have been so illuminating in diverse fields of inquiry. Even if the concept of progressive development — and historical contingency — is hardly new to anthropology, it is necessary to go beyond descriptive statistics or equilibrium models to explore historical contingency to break the seal of reification on the existing social order. Evolving networks are inevitably path dependent; future states are constrained by the past. But as new studies show, agency in the more powerful sense of the ability to shape genuine innovations can arise from the ordinary form of agency exhibited by people going about their daily business of commerce, marriage and politics.