In previous chapters the interactions were defined by the environment, by agents running around looking for resources, or by random interactions. These models did not include interactions that are not random as observed on real social systems.

Nowadays, many people are part of social network websites like Facebook or Myspace. Members are not connected by a random sample of other members, instead they are connected with their “friends”. If we look at networks on social network websites we will observe a structure. The structure of a network can affect a number of social phenomena. For example, the spread of a rumor. If a well-connected Facebook member put a rumor on her page, this information will spread much faster among the Facebook community when compared to a case in which the same rumor is put on the page of a person who has only one friend.

When we include network structures into our agent-based models we are able to study the effect of network structure on the diffusion of bits (information) and bugs (diseases). This will be examined in more detail in the next chapter. This chapter will discuss the basics of networks.