When our ancestors, hominids, were foraging 1 million years ago in Africa, they had to make decisions in complex environments. They had to make decisions what food items to eat, how to shelter themselves, where to go to in search for food, and whether and when to share food and coordinate hunting. Within small groups of hunter gatherers, knowledge was transmitted between generations and to remain in the group it was important to contribute a fair share of effort to the benefit of the group. Since the emergence of complex societies, our interactions with our environment and with each other have changed dramatically. Frequently our well-being is dependent on the actions of others, but more and more on the actions of “strangers”. When one was living in small groups there was a strong peer-pressure to cooperate. We developed cognitive mechanisms to judge trustworthiness of others and feel often good when we cooperate and treat others in a fair way. Nowadays we exchange products with strangers on the internet, which challenges our ability to judge the trustworthiness of others.

Social dilemmas refer to a class of dilemmas where there is a conflict between making a decision based upon the consequences for oneself and the group. In order to collect sufficient amount of tax money, avoid littering the streets and avoid overfishing of the oceans, we need cooperation of large groups of individuals. However, when many people will cooperate, it is beneficial for an individual to free ride on the cooperative actions of others.

The study of solving social dilemmas is a large field of inquiry in social simulation studies. This chapter provides a brief introduction to the basic literature, especially repeated games. We start to a discussion of two basic games.