Computer simulations are a new way of expressing theories of human behavior and societies. A theory is no longer expressed in words or mathematical symbols but it is used as a blueprint for constructing a computational artifact. If the artifact reproduces the available empirical data, the theory is confi rmed (Cangelosi and Parisi 1998, Cecconi and Parisi 1998). Furthermore, computer simulations can suggest new empirical data to look for and they can function as experimental laboratories in which the researcher varies the value of one or more variables and observes the effects of these variations.