Abstract. This paper presents a multi agent-oriented prototyping approach. It is a generic approach, applicable to a wide range of multi-agent systems. This approach relies on a few assumptions, the most important is that MAS must be described by an organizational model which semantics is given in term of a formal framework. This model allows for a simple description of both individual and collective multi-agent system aspects. The framework we use to give a formal description of this model is based on a multi-formalism approach. We illustrate this approach through a case study. Key words: Agent, Specification, Prototyping