A complex adaptive system (CAS) is a nonlinear, interactive, complex system with the ability to adapt to a changing environment. CAS's evolve by random mutation, self-organization, the transformation of their internal models of the environment, and natural selection. Examples include living organisms, the nervous system, the immune system, the economy, corporations, and societies. In a CAS, semi-autonomous agents interact according to certain rules of interaction, evolving to maximize some measure like fitness. The agents are diverse in form and capability and they adapt by changing their rules and, hence, behavior, as they gain experience. CAS's evolve historically – their experience determines their future trajectory. Their adaptability can either be increased or decreased by the rules shaping their interaction. Moreover, unanticipated, emergent structures can play a determining role in the evolution of such systems, which is why they are highly unpredictable. On the other hand, a CAS's have the potential of a great deal of creativity that was not programmed in to them from the beginning.