This paper presents a model of automatic negotiation agents in an open environment. Agents are motivated by the gain they may obtain while fulfilling their goals, but their behaviour can change during negotiation according to previous interactions with other agents in the system. Changing behaviour may refer to either the use of different negotiation strategies or to concessions made for other agents, with which they have successfully negotiated in the past. To this aim, an agent develops a set of partners’ profiles during negotiation: the preference profile, the cooperation profile, and the group negotiation profile. The first two profiles characterize individuals, while in a group negotiation profile, several agent profiles are clustered according to commonly discovered features. Different approaches to the development of these profiles are presented.