From The Economist:
The scientists and engineers who gathered this week in Oxford for the first International Workshop on Complex Agent-Based Dynamic Networks are seeking to explain much of the world’s behaviour through the use of agents. In this context, an agent is a program that acts in a self-interested manner in its dealings with numerous other agents inside a computer. This arrangement can mimic almost any interactive system: a stockmarket; a habitat; even a business supply-chain. If the constituent parts can be understood, the reasoning goes, some insight into the whole will follow.
The systems that agents have been most successful in modelling so far are financial markets. This is partly because of the obvious interest that people have in understanding such markets, and partly because one of the challenges in setting up an agent-based model is defining clearly what individual agents want. In a financial market that definition is easy: money.