The work achieved in multi-agent interactions design mostly relates to protocols definition, specification, etc. In this paper we tackle a new problem, the dynamic selection of interaction protocols. Generally the protocols and the roles agents play in protocol based interactions are imposed upon the system at design time. This static selection severely limits the openness, the dynamic behaviours agents are expected to exhibit, the integration of new protocols, etc. To address this issue, we developed a method which enables agents to select protocols themselves at runtime when they need to interact with one another. We define the concepts and the mechanisms which enable agents to perform this dynamic selection.