The social sciences study knowing subjects and their interactions. A "cog­ nitive turn", based on cognitive science, has the potential to enrich these sciences considerably. Cognitive economics belongs within this movement of the social sciences. It aims to take into account the cognitive processes of individuals in economic theory, both on the level of the agent and on the level of their dynamic interactions and the resulting collective phenomena. This is an ambitious research programme that aims to link two levels of com­ plexity: the level of cognitive phenomena as studied and tested by cognitive science, and the level of collective phenomena produced by the economic in­ teractions