Perhaps the one theoretical position available to archaeologists today that has the potential to integrate culture history, processualism, and post-processualism is the study of complexity and complex systems. Not to be confused with political complexity and the rise of social hierarchies, complexity theory is the study of how new complex properties emerge from the interactions of many agents interacting in often quite simple ways. But the properties that emerge from those simple interactions are nonlinear, complex, and not predictable from the study of the individual agents themselves. This chapter follows the recent publication of our book Complex Systems and Archaeology (Bentley and Maschner 2003a), and necessarily recapitulates much of its first three chapters. However, in the few years since that book was published, there was much for us to update, as complexity theory has grown at an accelerated rate (figure 15.1). (1) That commencing as small aggregations they insensibly augment in mass; some of them reaching eventually perhaps a hundred thousand times what they originally were; (2) That while at first so simple in structure as to be almost considered structureless, they assume, in the course of their growth, a continually increasing complexity of structure; (3) That through their early undeveloped state there exists in them scarcely any mutual dependence of parts, these parts gradually acquire a mutual dependence, which becomes at last so great, that the activity and life of each part is made possible only by the activity and life of the rest.