ABSTRACT
This chapter describes some of the complexity insights and their challenge to health economics. The period of the enlightenment that began in the late eighteenth century, was based on the confident assumption that the application of reason would expand knowledge and purge the residues of religion and mysticism. Human progress was to be achieved by a programme that extended scientific knowledge and technical control to all aspects of society. A complex system is a system of individual agents, who have the freedom to act in ways that are not always predictable, and whose actions are interconnected such that one agent's actions change the context for other agents. Agents operate according to their own internal rules or mental models - rules for how they respond to the environment. As agents can both change and share their internal rules, complex systems can learn and adapt over time.
