Several agent-oriented methodologies have been proposed over the last few years. Unlike the object-oriented domain and unfortunately for designers, most of the time, each methodology has its own purposes and few standardization works have been done yet, limiting the impact of agent design on the industrial world. This paper tries to find a means to unify three existing methodologies – ADELFE, Gaia and PASSI – by studying their meta-models and the concepts related to them. Comparing a certain number of features at the agent or system level (such as the agent structure, its society or organisation, its interactions capacities or how agents may be implemented) has enabled us to draw up a first version of a unified meta-model proposed as a first step towards interoperability between agent-oriented methodologies.