Considering the great number of agent-oriented methodologies that can be found in the literature, and the fact that each one defines its own concepts and system structure, one of the main challenges in agent-oriented software engineering (AOSE) research is how to make these methodologies interoperable. By defining concepts used in a specific domain in a non-ambiguous way, meta-modelling may represent a step towards such interoperability. Consequently the main objective of the AOSE TFG (Technical Forum Group) is to establish a strategy for identifying a common meta-model that could be widely adopted by the AOSE community. This paper sums up the approach used by this TFG which consists of (i) studying and comparing the meta-models related to some existing methodologies (ADELFE, Gaia, INGENIAS, PASSI, RICA and Tropos) in order to find commonalities and (ii) giving a clear and basic definition for the core concepts used in multi-agent systems for relating and positioning them in a unified MAS meta-model. The first proposal, set up by the working group, for this unified meta-model then concludes this paper.