In Agent Mediated Electronic Commerce, autonomy of agents is an important property. On one hand, it has to be favored to make the agents able to determine and adapt their own goals to the dynamic and open environment in which they are situated. On the other hand, it has to be controlled and limited to get a coherent and fruitful behavior in the system. In this paper we present a model of contract aiming at managing the cooperation between agents and at imposing a social order in the system : agents involved in a contract have to respect constraints related to others agents or to the society. This paper combines these notions with those of electronic contract in order to integrate agents within an eCommerce platform.