Abstract : This thesis describes two agent-based models that develop the emergence of relational patterns through exchange, and in particular trust and reputation. After reviewing the literature on trust, we describe these two models, which are based on observation of herdmen's behaviour in Nord-Cameroon when they negotiate their access to rangeland. To develop trust, these actors rely on three mechanisms: familiarity, reputation and the way they show themselves as reliable people through accepted behaviour. In the first model, herders trade access to land, and they choose their access according to two different memory: the representation of price and the representation of good relation ; in both cases some regularity emerges in their relations, but when they are interested in getting the lowest prices, land is destroyed very quickly, whereas the learning that relies on good relations creates more sustainable settings (mainly because of the reduction of competition). The second model follows a fielld study where reputation and social observation are shown to be very relevant. The model represents reputation building in a closed society. The main results is that no individual agent can get to a high reputation without a collective will that is interested in reputation building. As a conclusion, the way trust is built seems to be a good way to analyse official and unofficial norms of behaviour and to spot the social norms underlying exchanges. It is in particular a good approach to identify social norms that unable a group to have a sustainable use of a resource.